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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

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FORM 10-Q

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MESA OFFSHORE TRUST
(Exact name of Registrant as Specified in its Charter)

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        Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days. Yes ý No o

        Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes o No o

        Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act.

        Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes o No ý

        As of November 16, 2009—71,980,216 Units of Beneficial Interest were outstanding in Mesa Offshore Trust.

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PART I—FINANCIAL INFORMATION

Item 1.    Financial Statements.

MESA OFFSHORE TRUST

STATEMENTS OF DISTRIBUTABLE INCOME

(Unaudited)

STATEMENT OF ASSETS, LIABILITIES AND TRUST CORPUS

(The accompanying notes are an integral part of these financial statements.)

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MESA OFFSHORE TRUST

STATEMENTS OF CHANGES IN TRUST CORPUS

(Unaudited)

(The accompanying notes are an integral part of these financial statements.)

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MESA OFFSHORE TRUST

NOTES TO FINANCIAL STATEMENTS

(Unaudited)

Note 1—Trust Organization

The Trust

        The Mesa Offshore Trust (the "Trust") was created effective December 1, 1982. On that date, Mesa Petroleum Co., predecessor to Mesa Limited Partnership, which was the predecessor to MESA Inc., transferred to the Trust a 99.99% interest in the Mesa Offshore Royalty Partnership (the "Partnership"). The Trust is an independent trust administered by JPMorgan Chase Bank, N.A., as trustee (the "Trustee"). JPMorgan Chase Bank, N.A., was formerly known as The Chase Manhattan Bank and is the successor or "JPMorgan" by mergers to the original name of the Trustee, Texas Commerce Bank National Association.

        JPMorgan Chase & Co. and The Bank of New York Company ("BNY") announced in April 2006 an agreement pursuant to which BNY would acquire a portion of JPMorgan Chase & Co.'s corporate trust business in exchange for BNY's consumer small business and middle market banking business. This transaction did not include any transfer by JPMorgan of its obligations as Trustee of this Trust.

The Partnership

        The Partnership was created to receive and hold a net overriding royalty interest (the "Royalty") in ten producing and nonproducing oil and gas properties located in federal waters offshore Louisiana and Texas (the "Royalty Properties"). MESA Inc. created the Royalty out of its working interest in the Royalty Properties and transferred it to the Partnership. Until August 7, 1997, MESA Inc. owned and operated its assets through Mesa Operating Co. ("Mesa") the operator and the managing general partner of the Royalty Properties. On August 7, 1997, MESA Inc. merged with and into Pioneer Natural Resources Company ("PNRC"), formerly a wholly owned subsidiary of MESA Inc., and Parker & Parsley Petroleum Company merged with and into Pioneer Natural Resources USA, Inc. ("PNR") (successor to Mesa), a wholly owned subsidiary of PNRC (collectively, the mergers are referred to herein as the "Merger"). Subsequent to the Merger, PNR is the managing general partner of the Partnership. The Partnership is owned 99.99% by the Trust and 0.01% by PNR. PNR serves as the managing general partner of the Partnership. PNR receives no compensation for serving as managing general partner other than the income it receives attributable to its interest in the Partnership.

Note 2—Status of the Trust, Legal Proceedings, and Timing of Liquidation

Status of the Trust

        The Mesa Offshore Trust Indenture (the "Trust Indenture") provides that the Trust will liquidate if the total amount of cash per year received by the Trust falls below certain levels for each of three successive years. As a result of insufficient production on Royalty Properties nearing the end of their estimated productive lives, Royalty income received by the Trust in 2002, 2003 and 2004 fell below the Termination Threshold prescribed by the Trust Indenture. The Trustee had previously taken steps to begin the process of liquidating the Trust; however, the legal proceedings described herein directly challenged whether the Termination Threshold had in fact been met and thus affected the liquidation

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process, such that the Trustee initially delayed the sale of the Partnership's oil and gas assets in efforts to investigate and resolve the claims. However, due to the continuation of the litigation for more than four years, the related cost to the Trust, the threat that the properties might soon revert back to the Minerals Management Service ("MMS"), and the opportunity to realize greater proceeds for the benefit of the Trust estate, the Trustee concluded that a public auction of the Partnership's oil and gas assets was in the best interest of the Trust, and the Court had allowed a public auction of these assets to go forward. The Trustee therefore instructed Pioneer to proceed with a public auction of the Partnership's assets on March 18, 2009, and Pioneer complied; but there were no bids submitted at the auction, in the face of the pending litigation by the Plaintiffs described in "Legal Proceedings" below in this Note. The Trustee then provided notice of another public auction of the Partnership's oil and gas assets, to be held on August 12, 2009. However, this public auction did not go forward, based on a judgment dated August 6, 2009, in which the Court approved the parties' settlement agreement (as detailed in "Legal Proceedings" below in this Note), but held that there was an outstanding procedural issue that needed to be addressed prior to entry of final judgment. The parties to the settlement agreement therefore decided to postpone the sale of the Partnership's oil and gas assets until the Court entered final judgment resolving all issues in the litigation, which took place on September 14, 2009. In accordance with the final judgment and the settlement agreement, the Trustee instructed Pioneer to proceed with a public auction of the Partnership's assets on November 11, 2009. At the November 11, 2009 auction, the highest bidder for the Partnership's assets in the West Delta 61 Block was Emerald Energy, with a sales price of $700,000. The assets of the Partnership and Pioneer in the Brazos A-39 Block did not receive any bids in the auction. Pioneer is entitled to dispose of the Brazos A-39 Block assets in any manner it sees fit, and the Trustee is currently awaiting Pioneer's determination regarding how it will dispose of these assets and the timing for such dispositions, including potentially electing to plug and abandon the property. Any resulting sales proceeds will be remitted to the Trust as part of the wind-down process. See "—Timing of Liquidation" below in this Note. The Trustee, which has no authority or discretionary control over the timing of expenditures, production or income on the Royalty Properties, has no control over the occurrence of the Termination Threshold or its consequences.

Legal Proceedings

        On April 11, 2005, MOSH Holding, L.P. ("MOSH") filed an Original Petition in the District Court of Travis County, Texas, 250th Judicial District, against PNRC; PNR (together with PNRC, "Pioneer"); Woodside Energy (USA), Inc. ("Woodside"); and JPMorgan, as Trustee of the Mesa Offshore Trust (Case No. GN501113) (the "Lawsuit"). The Lawsuit was pending before the 334th Judicial District of Harris County, Texas (the "Court"). MOSH's Original Petition alleged Pioneer and Woodside are liable for various actions, including (1) a wrongful farmout by Pioneer to Woodside of the Brazos A-39 Lease, (2) a wrongful delay by Pioneer in producing the Brazos A-39 Lease and the Midway #5 well drilled thereon, (3) fraudulent accounting practices by Pioneer, (4) breach of fiduciary duty by Pioneer, (5) aiding and abetting breach of fiduciary duty by Woodside, (6) misapplication of Trust property by Pioneer, (7) conspiracy to misapply fiduciary property by Woodside and Pioneer, (8) common law fraud by Pioneer, (9) gross negligence by Pioneer, and (10) breach of the conveyance agreement by Pioneer. As described below, MOSH later added claims against the Trustee for (1) an accounting, and (2) breach of fiduciary duty. The remedies MOSH sought included (a) reconstruing the Trust Indenture to determine that the Trust is not terminated because there has or should have been production that would have generated revenues to extend the life of the Trust, (b) requiring the Trustee to pursue certain claims, or to allow MOSH to pursue such claims, (c) setting aside any farmouts by Pioneer in which there have been conveyances to an alleged affiliate of Pioneer, (d) the removal of JPMorgan as

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Trustee, (e) the return or forfeiture of compensation to JPMorgan, (f) monetary damages against Pioneer, Woodside and JPMorgan, and (g) unspecified exemplary damages against all defendants.

        MOSH's Original Petition did not contain any claims against the Trustee, except to enjoin the Trustee from terminating the Trust during the pendency of the Lawsuit. In April 2005, the Trustee entered into an agreement with MOSH whereby the Trustee would not sell the Trust assets without first giving MOSH 60-days written notice. This agreement allowed MOSH time to obtain documents and discovery from Pioneer and Woodside, and allowed the Trustee time to investigate the claims asserted by MOSH against Pioneer and Woodside to determine if they had any merit and, most importantly, whether the claims would benefit the Trust. During the six month period between April and October 2005, the Trustee conducted an independent investigation including: numerous meetings and discussions with the parties; reviewing the relevant documents with the Trustee's counsel; employing independent reservoir engineers to evaluate the reserves in which the Trust has an interest; engaging independent joint venture auditors to examine the accounting records of the operator, Pioneer, relating to revenues and expenses allocated to the Partnership's interests; and obtaining from both MOSH and Pioneer their respective legal analyses of the challenged farmout.

        Throughout 2005, the parties also anticipated that the Midway #5 well on the Brazos A-39 Lease that is the primary subject of the Lawsuit would go into production. Given the discrepancy between the reserves claimed by MOSH and those projected by Pioneer for the Midway #5 well, actual production results would significantly impact the Trustee's assessment of whether the Trust was better off with the cost-free override created by the Pioneer-Woodside farmout, or the prior cost-burdened net profits interest that MOSH seeks to restore through the Lawsuit. Unfortunately, Hurricane Katrina struck the Gulf of Mexico in August 2005 and delayed the commencement of production until 2006.

        Faced with this post-Katrina situation in the fall of 2005, the Trustee urged all the parties to consent to a bifurcated trial of the farmout issue on an expedited basis. The Trustee proposed to MOSH that if the Court determined that the farmout was not valid and that restoring the net profits interest would benefit the Trust, then the Trust would reimburse MOSH's reasonable attorneys' fees, up to $100,000, and the Trustee would allow MOSH's counsel to represent the Trust in prosecuting the damages portion of the case. Conversely, if MOSH were to lose on the expedited determination of the farmout issue, and in the absence of more evidence to support any ancillary claims, then MOSH would dismiss the other claims and would not be reimbursed, and the Trustee would move forward to terminate the Trust.

        Although the Trustee, Pioneer, and Woodside all agreed to an expedited trial of the farmout issues, MOSH balked. Contrary to the assertions of MOSH and the Intervenor Plaintiffs, the Trustee never agreed that the claims asserted by MOSH against Pioneer and Woodside "had merit"—the Trustee simply stated that the farmout issue might merit immediate adjudication at that time to determine if MOSH was legally correct.

        When MOSH refused to agree to an expedited and bifurcated trial as proposed by the Trustee, the Trustee informed MOSH that the Trustee's investigation of MOSH's allegations beyond the farmout issues failed to convince the Trustee that pursuing those claims and incurring the related legal fees and expenses would benefit the Trust. Moreover, the Trustee informed MOSH that the Trustee's independent joint venture auditors and reservoir engineers had not found any evidence to date to support any of MOSH's damage allegations. Therefore, the Trustee informed MOSH that the Trustee's investigation indicated that the Trust was better off with the post-farmout cost-free overriding royalty

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interest than the pre-farmout cost-burdened net profits interest, so the funding of MOSH's efforts to set aside the farmout with Trust funds would not be in the best interest of the Trust.

        It was at this point, in November 2005, in the midst of the Trustee's negotiations with MOSH to obtain an agreed resolution of MOSH's claims, that MOSH alleged for the first time that the Trustee had a conflict of interest because of JPMorgan's long-standing lending relationship with Pioneer. Although it is clear under the Trust Indenture, the Texas Trust Act, and relevant case law that JPMorgan is not precluded, by holding the position of Trustee, from pursuing commercial banking activities not involving Trust funds, MOSH amended its petition and asserted claims against the Trustee on November 28, 2005.

        Although it responded that MOSH's claims against the Trustee were meritless, to avoid any further assertion that the Trustee could not impartially evaluate MOSH's claims, on November 30, 2005, JPMorgan announced its intention to resign as Trustee, effective January 31, 2006. On December 13, 2005, the lawsuit was transferred to the 334th Judicial District Court of Harris County, Texas. At a hearing on January 27, 2006 in the Harris County Court, the Court denied MOSH's motion for a temporary injunction to remove JPMorgan as Trustee and appoint a principal of MOSH, Timothy Roberson, as a temporary Trustee. At the Court's suggestion, JPMorgan agreed to continue as Trustee, until such time as a substitute trustee was found that fulfilled the qualifications of Trustee stated in the Trust Indenture. Since that hearing, none of the parties ever identified a willing qualified successor Trustee that was not also a lender under one of Pioneer's credit facilities (which status MOSH contended was an alleged conflict of interest).

        On December 8, 2006, Dagger-Spine Hedgehog Corporation ("Dagger-Spine") filed a petition to intervene in the Lawsuit as a Plaintiff, alleging claims virtually identical to MOSH. Another group of unit holders, led by Keith A. Wiegand, (together with Dagger-Spine, the "Intervenors") also filed on March 9, 2007 a petition to intervene as plaintiffs in the Lawsuit, incorporating and adopting the same claims asserted by MOSH. MOSH and the Intervenors are referred to hereinafter as the "Plaintiffs."

        In 2006, after the Court denied MOSH's attempt to remove JPMorgan as Trustee, the parties pursued formal discovery in the Lawsuit. During this period, the Trustee continued to evaluate the merits of the alleged claims against Pioneer and Woodside. A central allegation by MOSH and the Intervenors was that Pioneer and Woodside delayed the commencement of production from the well drilled pursuant to the Pioneer-Woodside farmout—the Midway #5 well on the Brazos A-39 Lease. However, Woodside and Pioneer witnesses gave sworn testimony in depositions about the commercial and technical reasons for the delays in bringing the well on line. The well commenced production in April 2006. After production began, the Trustee instructed its independent petroleum reserve engineers to evaluate how the production results and projected future production from the well might affect the value of the Trust's interests. The Trustee's independent engineers determined that the initial production data from the well did not warrant a material change in prior assessments of the value of the Trust's assets.

        Pioneer subsequently reported to the Trustee that production from the well was suspended in July 2006 due to mercury contamination identified at downstream facilities where the production from the well is commingled with production from other wells. An updated evaluation from the Trustee's independent petroleum reserve engineers estimated that revenues from future production likely would not exceed the costs of drilling and completing the well. This confirmed to the Trustee that, if the Partnership's interest in the underlying lease had remained, or was, a cost-burdened net profits interest, instead of the cost-free overriding royalty interest the Partnership held as a result of the Pioneer-

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Woodside Farmout, the Partnership would not have received, or would not receive, any payments from this production, and the Trust accordingly would not have received any associated distributions. Further, the production data did not support reserves of the size asserted by the Plaintiffs. The well resumed production in February 2007, but the well was shut in again on April 18, 2007 due to an increase in hydrogen sulfide content coincidental with an increase in water production. Pioneer implemented a hydrogen sulfide contingency plan, which was required and approved by the MMS, including the installation of the necessary alarm and safety systems. The well was shut in October 4, 2008 after discovery of corrosion in the production separator on the host platform.

        A replacement production separator was installed on the host platform. The well was returned to production on March 19, 2009, but was subsequently shut in again on September 1, 2009, and has been off production ever since.

        Given its conclusion that the Trust was better off with the post-farmout override, and hoping to end this litigation and liquidate the Trust per the Trust Indenture, the Trustee reached a conditional settlement on January 26, 2007 with Pioneer and Woodside of the claims asserted by the Plaintiffs against Pioneer and Woodside. The conditional settlement was set forth in the Mutual Release and Settlement Agreement dated as of January 26, 2007 (the "Pioneer/Woodside Settlement Agreement"). The Trustee filed a motion for approval of the Pioneer/Woodside Settlement Agreement with the Court on January 30, 2007. The Trustee believed that the Pioneer/Woodside Settlement Agreement was in the best interest of the unit holders, but the Plaintiffs opposed it, and on June 19, 2007, the Court issued an Order denying the Trustee's motion to approve the Pioneer/Woodside Settlement Agreement.

        In June and July 2007, Pioneer and Woodside filed motions with the Court that argued that the claims against them did not have merit as a matter of law. Pioneer's motion included an argument that the Plaintiffs did not have the legal right to sue Pioneer because the claims belong to the Trust, not the beneficiaries of the Trust. On October 19, 2007, the Trustee offered to assign to the Plaintiffs the Trust's claims against Pioneer and Woodside, but the Plaintiffs rejected that offer. Through their counsel, the Plaintiffs and the Trustee also began negotiating a resolution of the claims pending between them, and on October 26, 2007, the Trustee and the Plaintiffs informed the Court of an agreement in principle to settle.

        On December 3, 2007, the Trustee entered into a Settlement Agreement and Release with the Plaintiffs and additional Trust unit holders (the "Plaintiffs' Settlement Agreement"). Also on December 3, 2007, the Trustee and the Plaintiffs filed a Joint Motion for Approval of Settlement Agreement (the "Joint Motion"). In response to the Joint Motion, on December 21, 2007, Pioneer filed cross-claims against the Trustee seeking declaratory and injunctive relief to prevent certain aspects of the proposed settlement between the Trustee and the Plaintiffs. On January 14, 2008, the Trustee filed an answer to Pioneer's cross-claims, in which the Trustee denied the cross-claims in their entirety, stated that they were baseless, and set forth numerous affirmative defenses. On January 22, 2008, the Court issued an Order denying the Joint Motion. As a result, the conditions precedent to the Plaintiffs' Settlement Agreement could not be satisfied, and the Plaintiffs' Settlement Agreement became null and void. In addition to denying the Joint Motion, the Court also considered and denied in the same Order (i) the application by the Plaintiffs for the appointment of a temporary trustee and (ii) Pioneer's application for a temporary restraining order. As a result of the Court's denial of the Joint Motion, and the Court's denial of the Plaintiffs' application for the appointment of a temporary trustee, JPMorgan elected not to resign in order to avoid a vacancy, and continues to serve as Trustee.

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        On April 28, 2008, the Court issued a Docket Control Order, setting the trial date for December 8, 2008. On July 3, 2008, the Plaintiffs filed a Third Amended Petition, seeking, among other things, to add claims against the Partnership (though its partners Pioneer and the Trustee) and JPMorgan in an individual capacity. By order dated July 3, 2008, the Court denied Pioneer's pending motions for summary judgment, including Pioneer's challenge to Plaintiffs' standing. Pioneer then filed a petition for writ of mandamus to the Houston Fourteenth Court of Appeals on July 22, 2008, seeking to reverse the trial courts' ruling on standing. On September 25, 2008, the Houston Fourteenth Court of Appeals denied Pioneer's petition for writ of mandamus, and Pioneer filed a petition for writ of mandamus with the Supreme Court of Texas on October 1, 2008. On October 24, 2008, the group of unit holders led by Keith A. Wiegand filed a Motion for Non-Suit Without Prejudice, and the Court granted the motion on October 24, 2008. Thus, all references herein to "Plaintiffs" after the date of October 24, 2008 include only MOSH and Dagger-Spine. At a hearing before the Court on October 31, 2008, the Plaintiffs agreed to postpone the trial again, and the trial was scheduled for April 13, 2009. The Supreme Court of Texas denied Pioneer's petition for writ of mandamus on November 21, 2008.

        By notice dated February 6, 2009, which the Trustee mailed to all unit holders of record on February 10, 2009, the Trustee announced again that the Termination Threshold had been met and that, as a result, it had instructed Pioneer to sell the oil and gas assets of the Partnership at public auction on March 18, 2009. In addition, the Trustee announced that the sale would include all of Pioneer's interests in Brazos Block A-39. On March 3, 9, and 12, respectively, unit holders Gordon Stamper, Robert Miles, and Keith Wiegand—formerly part of the group of Intervenors led by Keith Wiegand (collectively, the "Individual Intervenors")—filed pro se motions with the Court, requesting to intervene in the Lawsuit. At the public auction on March 18, 2009, no bids were submitted for the Partnership assets, in the face of the pending litigation with Plaintiffs. On March 25, 2009, Plaintiffs filed their Fourth Amended Original Petition, Application for Temporary Restraining Order, Temporary Injunction, Show Cause Order, and Permanent Injunction. On April 15, 2009 and May 9, 2009, respectively, unit holders Michael Brown and Benjamin Ginter filed additional interventions (collectively, along with other individuals previously defined as such, the "Individual Intervenors").

        On May 18, 2009, the Trustee, on behalf of the Trust, entered into a Final Settlement Agreement with (1) the Plaintiffs, both in their individual capacities and as claimed representatives of the Trust and/or the unit holders, (2) Pioneer and (3) Woodside. The terms of the Final Settlement Agreement include the following: (a) Pioneer will pay to the Trust $13 million and will sell and contribute to the Trust any proceeds from the sale of all of its interests in the Brazos Block A-39 (the "Pioneer Settlement Interests"); (b) Trustee will pay to the Trust $5 million and will release all claims for and forgive repayment of the existing $5 million Demand Promissory Note (the "Credit Facility") provided by JPMorgan, as lender, to the Trust; and (c) Woodside will pay to the Trust $1 million. Notwithstanding certain other releases, the Trustee will be permitted to use the remaining balance available under the Credit Facility and any other Trust income to pay Trust liabilities and expenses as permitted under the Trust Indenture prior to the final distribution of any net settlement proceeds. These liabilities and expenses include any out-of-pocket costs incurred for effecting the sale of assets in the Liquidation Process and for any other fees and expenses relating to the administration of the Trust after April 27, 2009. As provided in the Final Settlement Agreement, each of the parties agreed to release any and all claims against the other parties that are, or could have been, asserted in the Lawsuit, including any claims for reimbursement of attorney's fees or costs, except as provided for under the Final Settlement Agreement.

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        On June 15, 2009, a group of unit holders, most of whom were part of the former group led by Keith A. Wiegand that had previously voluntarily non-suited their claims, submitted a filing to the Court, seeking to delay certain issues from being heard at the June 18, 2009 settlement hearing. This group of unit holders is referred to herein as the "2009 Unit Holders." On June 18, 2009 and July 23, 2009, the Court held evidentiary hearings on the fairness of the Final Settlement Agreement. The purpose of these hearings was for the Court to determine whether the Final Settlement Agreement should be approved as being in the best interests of the Trust and its unit holders/beneficiaries. The Individual Intervenors, 2009 Unit Holders, and all other objectors were afforded the opportunity to participate in the hearings.

        The Court considered all of the papers filed, the evidence presented, and arguments both for and against the Final Settlement Agreement, and, on August 6, 2009, approved the Final Settlement Agreement and denied all objections thereto. In its Findings of Fact and Conclusions of Law With Respect to Final Settlement Agreement ("Findings of Fact and Conclusions of Law"), the Court ruled that all claims that were raised (or that could have been raised) against the defendants in the Lawsuit were owned by the Trust and/or the Partnership; the Plaintiffs pursued the claims asserted in the Lawsuit on behalf of the Trust and/or the Partnership; the Plaintiffs and the Trustee had the authority to prosecute, resolve, settle and release all released claims on behalf of the Trust, the Partnership and the Plaintiffs; and the settlement was in the best interest of the Trust and its unit holders. The Court also entered findings that full and proper notice of the Lawsuit, the Final Settlement Agreement, and the settlement fairness hearing was provided to all unit holders and that all unit holders were given the opportunity to obtain the related documents and express any objections they may have had regarding the Final Settlement Agreement. The Court considered these unit holder objections in entering the Findings of Fact and Conclusions of Law, and denied all of them.

        The initial judgment by the Court was interlocutory, meaning that it was not yet final, because, while the Court found that all unit holders were fully and properly notified of the Final Settlement Agreement and the related hearing, the Court indicated in its Findings of Fact and Conclusions of Law that it did not appear that the Individual Intervenors were provided notice that the motions to strike their petitions in intervention, filed by Pioneer, would be considered by the Court at the same time as the settlement agreement. Therefore, although the Court denied all of the Individual Intervenors' objections to the settlement, the Court also wanted to consider the related motions to strike their petitions in intervention before entering a final judgment in the Lawsuit.

        On July 10, 2009, the Trustee mailed a notice to all unit holders of record, announcing that the Termination Threshold had been met and that, in accordance with the Trust Indenture and Final Settlement Agreement, it had instructed Pioneer to sell the oil and gas assets of the Partnership at public auction on August 12, 2009 through The Oil & Gas Asset Clearinghouse, whose website is www.ogclearinghouse.com. However, given the interlocutory nature of the Court's August 6, 2009 judgment, the settling parties agreed to postpone the public auction until after the Court entered final judgment.

        On September 14, 2009, the Court signed its Final Judgment, resolving all parties and all claims in the Lawsuit. This Final Judgment granted the defendants' motion for summary judgment and motion to dismiss claims of Intervenors Keith Wiegand, Robert Miles, Gordon Stamper, Michael Brown, and Benjamin Ginter. Robert Miles non-suited his intervention prior to argument on these motions. The Final Judgment also denied the motion for sanctions filed by Gordon Stamper, and adopted and incorporated the August 6, 2009 Findings of Fact and Conclusions of Law. Thus, there are no longer

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any issues remaining before the Court, all objections to the Final Settlement Agreement are overruled and denied, all pending petitions in interventions are dismissed, and all related intervenors' claims are dismissed. Additionally, all other claims by parties to the Lawsuit, to the extent not otherwise addressed by the Final Judgment, are dismissed with prejudice. On October 19, 2009, Gordon Stamper filed a petition for writ of mandamus in the Houston Fourteenth Court of Appeals, related to a September 10, 2009 order denying his motion to recuse the Judge presiding over the Lawsuit. The Houston Fourteenth Court of Appeals denied his petition for writ of mandamus in an opinion dated November 3, 2009. Also on November 3, 2009, Gordon Stamper filed a "Motion to Appeal" in the Court, and this Motion has been assigned to the Houston Fourteenth Court of Appeals.

        Given the entry of the Final Judgment, the Trustee directed Pioneer to sell the assets of the Mesa Offshore Royalty Partnership (the "Partnership assets") (along with the Pioneer Settlement Interests), consistent with the terms contained in the Final Settlement Agreement, and as approved by the Court in the Final Judgment, at public auction on November 11, 2009 through The Oil & Gas Asset Clearinghouse, whose website is www.ogclearinghouse.com. Notice of the public auction was mailed to the unit holders of record at least thirty days before the sale.

        At the public auction, the Partnership assets and the assets contributed to the Trust by Pioneer for sale pursuant to its tender letter of October 10, 2008 (hereafter referred to as "Pioneer Settlement Interests") were offered in two lots: (1) the West Delta 61 Lot; and (2) the Brazos A-39 Lot (together, the "Sales Lots"). There was no right of first refusal as previously considered, and the two lots were offered for sale to the highest bidder(s). The highest bidder for the West Delta 61 Lot was Emerald Energy, with a purchase price of $700,000. The Brazos A-39 Lot, including interests owned by the Partnership and assets contributed to the Trust by Pioneer for sale pursuant to a tender letter, did not receive any bids. Since this liquidation process did not result in the sale of Pioneer's interests in Brazos Block A-39, Pioneer is entitled to dispose of such assets in any manner it sees fit, including by way of example and without limitation, withdrawing from participation in and ownership in Brazos Block A-39 pursuant to the terms of the Offshore Operating Agreement governing this property. In addition, if the Partnership's interests remain unsold and no buyer can be found, Pioneer has the absolute right to cancel and/or extinguish such interests. Until the time of the sale or abandonment of the Partnership's assets, Pioneer, as managing general partner of the Partnership, will continue to operate the Partnership's assets and distribute in the normal course any net proceeds to the Trustee for the benefit of the Trust. The Trustee is currently awaiting Pioneer's determination regarding how it will dispose of the Partnership's and Pioneer's interests in the Brazos A-39 Lot and the timing for such dispositions, including potentially electing to plug and abandon the property.

        The Trustee expects to establish a future record date after the West Delta 61 Lot sale and the final sale or abandonment of the interests in the Brazos A-39 Lot, and the concurrent termination of the Trust in accordance with the Trust indenture. This record date will serve as the date for holders of record entitled to final distributions as part of the winding up of the Trust. After such date, the Trustee will not recognize any subsequent transfers of Trust units. The Trustee will also request the termination of trading of Trust units on the OTC Bulletin Board and transfers of beneficial interests by The Depository Trust Company (DTC) for its participants on or prior to such final record date.

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        Under the terms of the Final Settlement Agreement, payment of the settlement proceeds by Pioneer, JPMorgan and Woodside into escrow will occur within seven business days after the date of the public auction. The settlement proceeds will be placed into separate, interest-bearing, escrow accounts at JPMorgan and will not be distributed by the Trustee until the Final Judgment becomes final and non-appealable. Should the Final Judgment be reversed, the settlement proceeds will be returned to the respective defendants.

        The final distribution by the Trust of the proceeds (i.e., the settlement proceeds plus any sales proceeds from the public auction of the Partnership assets and the Pioneer Settlement Interests) to Trust unit holders will be made only after the settlement proceeds have been remitted to the Trustee, and the Trustee has deducted any costs incurred for effecting the sale of assets in the liquidation process and any other fees and expenses relating to the administration of the Trust after April 27, 2009. Also, in accordance with the Final Judgment, counsel for the Plaintiffs have been awarded attorney's fees and expenses of $7,750,000, which will be paid and deducted before final distribution. Accordingly, the final distribution of net settlement and sales proceeds by the Trust to its 71,980,216 outstanding units of beneficial interest may be materially less than the gross settlement and sales proceeds.

        For more information regarding the estimated remaining life of each of the Royalty Properties, the estimated future net revenues of the Royalty Properties and information relating to farm-outs of interests on the Royalty Properties, see Item 1A. "Risk Factors" of the Form 10-K for the year ended December 31, 2008 and Note 8 in the Notes to Financial Statements included elsewhere in the Form 10-K. The final distribution to unit holders will be an amount net of funds required to satisfy all Trust liabilities.

Timing of Liquidation

        The Trust Indenture provides the Trustee a two-year period during which it must sell all of the assets of the Partnership. The Trust Indenture provides that such properties must be sold for cash and not for any other consideration. The sale process will be open to any persons desiring to participate, but as is customary, access to information and participation may be limited to persons who execute confidentiality agreements regarding information provided by the working interest owners. The Trustee may also require bidders to identify themselves clearly and to represent or evidence sufficient financing in order to participate, as the Trustee expects payment will be required promptly after the close of bidding without any financing conditions. Accordingly, the auction may not be a "public" auction in the sense that it may not be open to anyone who does not satisfy these requirements.

Note 3—Going Concern

        The accompanying financial statements have been prepared assuming that the Trust will continue as a going concern. The Trust Indenture provides that the Trust will liquidate if the total amount of cash per year received by the Trust falls below certain levels for each of three successive years. As a result of insufficient production on Royalty Properties nearing the end of their estimated productive lives, Royalty income received by the Trust in 2002, 2003, and 2004 fell below the Termination Threshold prescribed by the Trust Indenture. In 2005, the Trustee began procedures to liquidate the Trust's assets. Once the Trustee has liquidated all of the Trust's assets and has met all its obligations as described in the Trust Indenture, the Trust will no longer be a viable entity.

        During the two years ended December 31, 2008, the Trust incurred general and administrative expenses which exceeded Royalty and interest income and its available cash reserves, due to the

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absence of royalty income and expenses incurred in connection with the ongoing litigation. As such, the Trustee was required to borrow money in accordance with the Trust Indenture to fund Trust expenses. The Trustee entered into a Demand Promissory Note with JPMorgan on September 28, 2007, which was amended on December 3, 2007, for demand loans that may be advanced from time to time in the principal amount of up to $3 million. The amendment provided for, among other provisions, an extension of the stated maturity date of the Loans made pursuant to the Demand Promissory Note and the Amended and Restated Note until the earlier of (1) December 31, 2009, (2) 31 days after the Trust's receipt of any settlement proceeds, recovery or judgment in connection with the Lawsuit, (3) final liquidation of the Trust's assets, or (4) the Plaintiffs' Settlement Agreement is not approved by the Court.

        On January 22, 2008, the court in which the lawsuit was pending issued an Order denying a Joint Motion for approval of Settlement Agreement. According to the terms of the Amended Promissory Note, the note matured on this date as a result of the denial, and all portions of the outstanding principal under this note together with accrued and unpaid interest became due, in full. However, on August 25, 2008, in connection with the execution of the Second Amended and Restated Promissory Note, the definition of "Maturity Date" was amended to delete the test relating to the failure of the Court to approve the prior Settlement Agreement. As a result, the due date of the Demand Promissory Note was not accelerated as a result of the order described above, however, the maturity date remained (1) December 31, 2009, (2) 31 days after the Trust's receipt of settlement proceeds, recovery or judgment in connection with the Lawsuit or (3) final liquidation of the Trust's assets.

        On January 28, 2009, the Trustee executed and delivered to JPMorgan a Third Amended and Restated Promissory Note, dated as of January 12, 2009, increasing the principal amount available for borrowing, subject to the terms of such note, to $5 million. As of September 30, 2009, there was outstanding $5,260,198 advanced by JPMorgan, including $5.0 million under the Demand Promissory Note, for payment of Trust expenses together with $410,676 of accrued and unpaid interest expense. At September 30, 2009, the Trust had $0 available under this facility, but $382,741 in trust expenses payable. No assurance can be given that the Trustee will be able to borrow money on terms the Trustee considers reasonable or at all. The Trust intends to pay existing unpaid expenses and future expenses in excess of royalty income through the use of proceeds from the Final Settlement Agreement, or from the sale of the Trust's assets.

        Currently, the Trust does not have the cash resources available to repay the debt or expenses payable. This raises substantial doubt regarding the Trust's ability to continue as a going concern. The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Note 4—Net Overriding Royalty Interest

        The instruments conveying the Royalty to the Partnership provide that PNR will calculate and pay to the Partnership each month an amount equal to 90% of aggregate net proceeds for the preceding month. Generally, net proceeds means the excess of the amounts received by PNR from sales of its share of oil and gas from the Royalty Properties (gross proceeds) over the operating and capital costs incurred. Costs exceeding gross proceeds for any month are recovered by PNR, with interest thereon at the prime rate of the Bank of America plus one-half percent, out of future gross proceeds prior to making further Royalty payments to the Partnership.

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        Amortization of the Royalty, which is calculated on the basis of current Royalty income in relation to estimated future Royalty income, is charged directly to trust corpus since such amounts do not affect distributable income.

Note 5—Basis of Presentation

        The accompanying unaudited financial information has been prepared by the Trustee in accordance with the instructions to Form 10-Q. JPMorgan was formerly known as The Chase Manhattan Bank and is the successor by mergers to the original name of the Trustee, Texas Commerce Bank National Association. The preparation of the financial statements requires estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period.

        Actual results could differ from those estimates. The Trustee believes such information includes all the disclosures necessary to make the information presented not misleading. The information furnished reflects all adjustments which are, in the opinion of the Trustee, necessary for a fair presentation of the results for the interim periods presented. The financial information should be read in conjunction with the financial statements and notes thereto included in the Trust's 2008 Annual Report on Form 10-K. Subsequent events have been evaluated through November 16, 2009, the date of the issuance of these financial statements.

        The financial statements of the Trust do not include any adjustment as a result of the termination of the Trust as described in notes 1, 2 and 3 and are prepared on the following basis:

        (a)   Royalty income recorded for a month is the Trust's interest in the amount computed and paid by the working interest owner to the Partnership for such month rather than either the value of a portion of the oil and gas produced by the working interest owner for such month or the amount subsequently determined to be 90% of the net proceeds for such month;

        (b)   Interest income, interest receivable and distributions payable to unit holders include interest to be earned on short-term investments from the financial statement date through the next date of distribution; and

        (c)   Trust general and administrative expenses, net of reimbursements, are recorded in the month they accrue and are recoupable from Royalty income. Trust expenses payable and the note payable are reported as a reduction in Trust Corpus.

        This basis for reporting distributable income is considered to be the most meaningful because distributions to the unit holders for a month are based on net cash receipts for such month. However, it will differ from the basis used for financial statements prepared in accordance with accounting principles generally accepted in the United States because, under such accounting principles, royalty income for a month would be based on net proceeds from sales for such month without regard to when calculated or received and interest income for a month would be calculated only through the end of such month, and accounting principles generally accepted in the United States would require a liquidation basis of accounting.

        The instruments conveying the Royalty provide that the working interest owner will calculate and pay the Partnership each month an amount equal to 90% of the net proceeds for the preceding month. Generally, net proceeds means the excess of the amounts received by the working interest owner from sales of oil and gas from the Royalty Properties plus other cash receipts over operating and capital

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costs incurred. PNR believes all major abandonment charges have been incurred. On December 18, 2008, PNR informed the Trustee that there is no longer a deficit balance due for abandonment accrual for amounts expended and for projected future abandonment expenses for the properties in which the Trust has an interest.

        During the three and nine months ended September 30, 2009, the Trust received $86,113 and $301,243, respectively, in Royalty income; however, no Royalty income will be distributed to unit holders until the Trustee recoups Trust expenses being paid from the reserve that the Trustee has established for anticipated future general and administrative expenses and any loans secured by the Trustee to pay Trust expenses are repaid in full. As of September 30, 2009, approximately $6.1 million will be recouped by the Trustee from future Royalty income before Trust distributions will resume. During the three and nine months ended September 30, 2009 and 2008, the Trust had no distributable income. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan were used to pay $215,587 of the Trust's general and administrative expenses of $373,326 for the three months ended September 30, 2009 and $249,641 of accrued expenses from the first quarter of 2009. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan were used to pay $1,605,829 of the Trust's general and administrative expenses of $2,068,479 for the nine months ended September 30, 2009, and $270,595 of accrued expenses from 2008. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan were used to pay $673,383 of the Trust's general and administrative expenses of $535,254 for the three months ended September 30, 2008 and $146,245 of accrued expenses from the second quarter of 2008. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan and other advances were used to pay $1,646,962 of the Trust's general and administrative expenses of $1,576,015 for the nine months ended September 30, 2008 and $190,955 of accrued expenses from 2007. The Trust had unpaid expenses of $382,741 and $120,008 as of September 30, 2009 and 2008, respectively.

        Below is a summary of general and administrative expenses and the adjustments made to the reserve for Trust expenses:

Note 6—JPMorgan Demand Promissory Note

        On September 28, 2007, the Trust entered into a Demand Promissory Note agreement with JPMorgan in order to cover portions of its operating expenses. The lender approved an uncommitted line of credit to the Trust in a principal amount not to exceed $3 million. As part of the agreement,

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JPMorgan pays the expenses on behalf of the Trust. JPMorgan may decline to fund any request of the Trust for borrowings at anytime, for any reason, including the event that JPMorgan has reason to believe that the Trust will not be able to satisfy its obligation to repay the Demand Loans. Interest on the note is calculated at a rate per annum equal to Prime Rate plus two percent (2%), paid annually. The Demand Promissory Note is secured by a pledge of the Trust Estate, as that term is defined in the Trust Indenture, including without limitation the 99.99% general partnership interest in the Mesa Offshore Royalty Partnership owned by the Trust, pursuant to a Pledge Agreement dated September 29, 2007, as amended by the First Amendment to Pledge Agreement dated as of December 3, 2007, executed by the Trust for the benefit of the Lender. The Trust may borrow amounts under this Note until such time as JPMorgan makes demand for payment in full or December 31, 2008, whichever is earlier.

        On December 3, 2007, JPMorgan, individually and as lender, entered into an Amended and Restated Promissory Note with the Trust as borrower, to amend the Demand Promissory Note to provide for, among other provisions, an extension of the stated maturity date of the Loans made pursuant to the Demand Promissory Note and the Amended and Restated Note until the earlier of (1) December 31, 2009, (2) 31 days after the Trust's receipt of any settlement proceeds, recovery or judgment in connection with the Lawsuit, (3) final liquidation of the Trust's assets, or (4) the Plaintiffs' Settlement Agreement is not approved by the Court. Additionally, the amendment provided that the Trust may continue to obtain loans under the note until the maturity date, as long as the amount borrowed does not exceed $3 million and the loan is not in default. The amendment also provided that interest expense shall be due and payable on the maturity date.

        On August 25, 2008, the Trustee executed an amended and restated Demand Promissory Note that among other things increased the aggregate principal amount available for borrowing to $4 million and amended the definition of "Maturity Date" to delete the text relating to the failure of the Court to approve the prior Settlement Agreement.

        On January 28, 2009, the Trustee executed and delivered to the lender a Third Amended and Restated Promissory Note, dated as of January 12, 2009, increasing the principal amount available for borrowing, subject to the terms of such note, to $5 million. On January 28, 2009, the Trust and JPMorgan Chase Bank, N.A. also entered into a Third Amendment to Pledge Agreement, dated as of January 12, 2009, amending the definition of "Collateral" from the Second Amendment to the Pledge Agreement dated June 25, 2008 to include (1) all issued and outstanding general partnership interests by the Trust in the Partnership, together with any cash or property received in exchange or in substitution for such interests (collectively, the "Pledged Assets"), and any distributions received on such Pledged Assets or cash or property received upon any conversion or in exchange for such Pledged Assets; (2) all Additional Collateral (as defined therein) owned by the Trust; (3) all deposit accounts in the name of the Trust; (4) any consideration received or due to the Trust; and (5) all proceeds of any and all of the foregoing.

        Interest is payable at a base rate offered by JPMorgan as announced publicly at its principal office as its prime commercial lending rate, plus 2%. The rate effective as of September 30, 2009 was a Prime Rate of 3.25%, plus 2% for a combined rate of 5.25%.

        As of September 30, 2009, there was outstanding $5,260,198 of principal advanced for payment of Trust expenses (including $5.0 million under the Demand Promissory Note) together with $410,676 of accrued and unpaid interest expense. At September 30, 2009, the Trust had $0 available under this facility. No assurance can be given that the Trustee will be able to borrow money on terms the Trustee

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considers reasonable or at all. As noted above, JPMorgan has no further obligation to advance additional monies to the Trust and as of November 16, 2009, $5,260,198 remains payable to JPMorgan.

Note 7—Distributions to Unit holders

        Under the terms of the Trust Indenture, the Trustee must distribute to the unit holders all cash receipts, after paying liabilities and providing for cash reserves as determined necessary by the Trustee.

        The amounts distributed are determined on a monthly basis and are payable to unit holders of record as of the last business day of each month. However, cash distributions are made quarterly in January, April, July and October, and include interest earned from the monthly record dates to the dates of distribution.

Note 8—Federal Income Taxes

        The Trustee reports on the basis that the Trust is a grantor trust. Based on its previous audit policy, the Internal Revenue Service (the "IRS") is expected to concur with such action. No IRS ruling has been received or requested with respect to the Trust, however, and no court case has been decided involving identical facts and circumstances. It is possible, therefore, that the IRS would assert upon audit that the Trust is taxable as a corporation and that a court might agree with such assertion.

        As a grantor trust, the Trust will incur no federal income tax liability. In addition, it will incur little or no federal income tax liability if it is held to be a non-grantor trust. If the Trust were held to be taxable as a corporation, it would have to pay tax on its net taxable income at the corporate rate.

        The Trustee assumes that some Trust Units are held by a middleman, as such term is broadly defined in U.S. Treasury Regulations (and includes custodians, nominees, certain joint owners, and brokers holding an interest for a custodian in street name). Therefore, the Trustee considers the Trust to be a non-mortgage widely held fixed investment trust ("WHFIT") for U.S. federal income tax purposes. Bank of New York Trust Company, N.A., 919 Congress Avenue, Austin, Texas 78701, telephone number 1-800-852-1422, is the representative of the Trust that will provide tax information in accordance with applicable U.S. Treasury Regulations governing the information reporting requirements of the Trust as a WHFIT.

Note 9—Recently Issued Pronouncements

        In December 2008, the SEC announced that it had approved revisions designed to modernize the oil and gas company reserve reporting requirements. The most significant amendments to the requirements include the following:

•

commodity prices—economic producibility of reserves and discounted cash flows will be based on a 12-month average commodity price unless contractual arrangements designate the price to be used;



•

disclosure of unproved reserves—probable and possible reserves may be disclosed separately on a voluntary basis;



•

proved undeveloped reserve guidelines—reserves may be classified as proved undeveloped if there is a high degree of confidence that the quantities will be recovered;

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•

reserve estimation using new technologies—reserves may be estimated through the use of reliable technology in addition to flow tests and production history; and



•

nontraditional resources—the definition of oil and gas producing activities will expand and focus on the marketable product rather than the method of extraction.

        The rules are effective for fiscal years ending on or after December 31, 2009, and early adoption is not permitted. The Trust is currently evaluating the new SEC rules and proposed FASB Accounting Standards Update assessing the impact they will have on its reported oil and gas reserves. The SEC is coordinating with the FASB to obtain the revisions necessary to U.S. GAAP concerning financial accounting and reporting by oil and gas producing companies and disclosures about oil and gas producing activities to provide consistency with the new rules. During September 2009, the FASB issued an exposure draft of a proposed Accounting Standards Update "Oil and Gas Reserves Estimation and Disclosures." The proposed update would amend existing standards to align the reserves calculation and disclosure requirements in the SEC rules. As proposed, the update would be effective for annual reporting periods ending on or after December 31, 2009, and would be applied prospectively as a change in estimate.

        In June 2009, the FASB established the FASB Accounting Standards Codification (Codification), which officially commenced July 1, 2009, to become the source of authoritative US GAAP recognized by the FASB to be applied by nongovernmental entities. Rules and interpretive releases of the SEC under authority of federal securities laws are also sources of authoritative US GAAP for SEC registrants. Generally, the Codification is not expected to change US GAAP. All other accounting literature excluded from the Codification will be considered nonauthoritative. The Codification is effective for financial statements issued for interim and annual periods ending after September 15, 2009. We adopted the new standards for our quarter ending September 30, 2009. All references to authoritative accounting literature are now referenced in accordance with the Codification.

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Item 2.    Management's Discussion and Analysis of Financial Condition and Results of Operations.

        The following review of the Trust's financial condition and results of operations should be read in conjunction with the financial statements and notes thereto.

Note Regarding Forward-Looking Statements

        This Form 10-Q includes "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements other than statements of historical facts included in this Form 10-Q, including without limitation the statements under "Management's Discussion and Analysis of Financial Condition and Results of Operations" are forward-looking statements. Although Pioneer has advised the Trust that it believes that the expectations reflected in such forward-looking statements are reasonable, no assurance can be given that such expectations will prove to have been correct. Important factors that could cause actual results to differ materially from expectations ("Cautionary Statements") are disclosed in this Form 10-Q, including, without limitation, in conjunction with the forward-looking statements included in this Form 10-Q and in the Trust's Form 10-K for the year ended 2008, including under Item 1A. "Risk Factors." All subsequent written and oral forward-looking statements attributable to the Trust or persons acting on its behalf are expressly qualified in their entirety by the Cautionary Statements.

Financial Review

        The amount of cash distributed by the Trust is dependent on, among other things, the sales prices and quantities of gas, crude oil, condensate and natural gas liquids produced from the Royalty Properties and the quantities sold. Substantial uncertainties exist with regard to future gas and oil prices, which are subject to fluctuations due to the regional supply and demand for natural gas and oil, production levels and other activities of the Organization of the Petroleum Exporting Countries ("OPEC") and other oil and gas producers, weather, storage levels, industrial growth, conservation measures, competition and other variables.

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        Below is a summary of Royalty income received on the Trust properties for the three months and nine months ended September 30, 2009 and 2008:

        Below is a summary of distributable income for the three and nine months ended September 30, 2009 and 2008:

        During the first, second and third quarters of 2009 and 2008, the Trust had no distributable income. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan and other advances were used to pay $215,587 of the Trust's general and administrative expenses of $373,326 for the three months ended September 30, 2009 and $249,601 of accrued expenses from the second quarter of 2009. The reserve for Trust expenses and advances under the Demand Promissory Note and other advances with JPMorgan were used to pay $1,605,829 of the Trust's general and administrative expenses of $2,068,479 for the nine months ended September 30, 2009, and $270,595 of accrued expenses from 2008. The reserve for Trust expenses and advances under the Demand Promissory Note with JPMorgan were used to pay $673,383 of the Trust's general and administrative expenses of $535,254 for the three months ended September 30, 2008 and $146,245 of accrued expenses from the second quarter of 2008. The reserve for Trust expenses and advances under the Demand

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Promissory Note with JPMorgan were used to pay $1,646,962 of the Trust's general and administrative expenses of $1,576,015 for the nine months ended September 30, 2008 and $190,955 of accrued expenses from 2007. The Trust had unpaid expenses of $382,741 and $120,008 as of September 30, 2009 and 2008, respectively.

        On September 28, 2007 the Trust entered into a Demand Promissory Note with JPMorgan which was amended on December 3, 2007, August 25, 2008 and January 12, 2009, in which loans will be advanced by the lender from time to time not to exceed $5 million. This Demand Promissory Note will be used to pay any unpaid administrative expenses related to the operation of the Trust. As of September 30, 2009, $5,260,198 has been advanced to the Trust to pay Trust expenses, including $5.0 million under the Demand Promissory Note.

        Below is a summary of general and administrative expenses and the adjustments made to the reserve for Trust expenses:

        General and administrative expenses of the Trust incurred during the third quarter of 2009 decreased $161,928 or 30% to $373,326 as compared to $535,254 for the same period in 2008. General and administrative expenses of the Trust for the nine months ended September 30, 2009, increased $492,464 or 31% to $2,068,479 compared to $1,576,015 for the first nine months of 2008. The increase in general and administrative expenses in the nine months ended September 30, 2009 is primarily due to an increase in legal fees as a result of pending litigation and expenditures related to the anticipated sale of Trust properties pursuant to the Trust's termination.

Operational Review

        PNR has advised the Trust that during the third quarter of 2009 and 2008 its offshore gas production was marketed under short-term contracts at spot market prices primarily to TOTAL S.A. and that it expects to continue to market its production under short-term contracts for the foreseeable future. Spot market prices for natural gas in the third quarter of 2009 were generally lower than spot market prices in the third quarter of 2008.

        The amount of cash distributed by the Trust is dependent on, among other things, the sales prices and quantities of gas, crude oil and condensate produced from the Royalty Properties and the quantities sold. Substantial uncertainties exist with regard to future gas and oil prices, which are subject

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to fluctuations due to the regional supply and demand for natural gas and oil, production levels and other activities of the Organization of the Petroleum Exporting Countries ("OPEC") and other oil and gas producers, weather, storage levels, industrial growth, conservation measures, competition and other variables.

        Below is an operational review of the remaining producing Trust properties:

Brazos A-7 and A-39

        The Brazos A-39 block continued to experience a decrease in natural gas production due to natural production decline. As of September 30, 2009, this block had one well capable of producing, the Brazos A-39 #5 which was shut-in during the first quarter of 2007 due to the detection of mercury. The Brazos A-7 #B-1 well, operated by Newfield, was no longer producing and abandoned in 2007. PNR previously entered into farmout agreements for the Partnership's interest in both of these blocks so that two exploration prospects could be drilled and in which the Trust will retain an overriding royalty interest. The first prospect on Brazos A-7 was drilled during 2003 and was determined to be a dry hole. As such, the well was plugged and abandoned.

        The second exploration prospect, the Brazos A-39 #5 well, was drilled on Brazos A-39, which PNR announced as a discovery. A production test was completed in 2005. PNR, the operator on this property, informed the Trustee that the lower horizon of the prospect was determined to be non-commercial, while the middle horizon in the Big Hum 4 sand produced at 10,000 Mcf of gas per day during a seventeen hour flow test. This well came on line April 20, 2006. However, this well has been shut in from time to time since then as the operator has encountered and addressed hydrogen sulfide issues. The well has also produced a carbon dioxide content that exceeds pipeline specifications. This higher content requires the operator to mix production at the platform with production from other fields in order to transport the product. Production is being routed to the A-52C platform owned by Beryl Oil and Gas. That platform is being operated by Arena, which is also serving as the contract operator for the Midway property. The well was shut in July 21, 2006 by Williams Pipeline due to reported detection of mercury in the gas stream. Following the installation of vessels with mercury absorbing media and negotiation of the required agreements with the owner and operator of the Brazos A-52C host platform, the well was returned to production on February 13, 2007. The well was shut-in on April 18, 2007 due to an increase in hydrogen sulfide content coincidental with an increase in water production. Pioneer implemented a hydrogen sulfide contingency plan, which was required and approved by the Minerals Management Service ("MMS"), including the installation of the necessary alarm and safety systems. The well was shut in October 4, 2008 after discovery of corrosion in the production separator on the host platform. A replacement production separator was installed on the host platform. The well was returned to production on March 19, 2009. The well was producing at a

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rate of approximately 1.5 MM/D with a gradually declining flowing tubing pressure; however, there was no assurance regarding the longevity of the gas production on the 52C host platform. Blending with this gas is required to meet pipeline gas quality specifications. Since September 1, 2009, Arena's well has not been producing and as a result, the PNR well is shut-in.

        Arena has made several attempts to unload accumulated fluid from the well and return it to production with no results to date. Arena is currently evaluating additional options including economics associated with these options. Arena will advise when they have decided on next steps, if any, to return the well to production.

        Under the terms of a farmout agreement between PNR and Woodside, PNR farmed out to Woodside the undivided one-half interest previously burdened by the Partnership's net profits interest, but expressly providing that the farmed out interest would not be subject to the Partnership's net profits interest. PNR reserved a 10% overriding royalty interest, proportionately reduced to the interest conveyed, which interest, upon Woodside's recoupment of specified costs and expenses, would increase to 12.5%, proportionately reduced to the interest conveyed. The Partnership's net profits interest burdens the overriding royalty interest reserved by PNR. PNR has informed the Trustee that it believes this process is consistent with the terms of the original conveyance and with the handling of other farmout transactions involving lands burdened by the Partnership's net profits interest.

        PNR continues to own the undivided one-half interest not burdened by the Partnership's net profits interest and will participate in and operate the well as owner of that undivided one-half interest (subject to an agreement with Woodside to grant Woodside such interest in PNR's remaining undivided one-half interest to equalize those parties' participation in the well).

        PNR has noted to the Trustee that the farmout agreement with Woodside enabled the drilling costs of these prospects to be carried on the Partnership's interest in part by Woodside. PNR further noted that the Partnership's net profits interest would not have entitled the Trust (through the Partnership) to payment until drilling costs and applicable interest were recovered, whereas the overriding royalty interest retained under the farmout agreement entitles the Trust (through the Partnership) to payments prior to the recoupment of expenses incurred by Woodside and PNR. As noted above, the first prospect on Brazos A-7 was determined to be a dry hole. Under the farmout agreement and related agreements, those drilling and abandonment costs have been born entirely by PNR and Woodside and are not subject to recoupment from any proceeds otherwise payable to the Partnership or the Trust. Similarly, the Partnership's current interest in the "Midway" prospect on Brazos A-39 will be entitled to payment prior to PNR's and Woodside's recovery of expenses for drilling, completion, sub-sea tie backs and other costs.

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West Delta 61 and Other

        There are currently three wells producing on this block, and their combined rate is 1.0 MMcf/day and 100 barrels of oil per day.

        The PNR-operated wells ceased production in 2002, and the wells were plugged and abandoned by year-end with the facilities being completely abandoned during 2003. The only remaining wells on this block are in West Delta 61. PNR farmed out a portion of West Delta 61 to Stone Energy retaining a 12.5% (11.25% net to the Trust through the Partnership) overriding royalty interest. Those properties were sold to Maritech Resources Inc. effective October 1, 2007. Maritech began accounting for the properties on February 1, 2008.

Capital Expenditures

        The Trustee has been advised that PNR does not anticipate any significant capital expenditures on the Royalty Properties in the future. Due to the limited financial capacity of the Trust, PNR has advised that it intends to farm out the Partnership's interest in the blocks it believes may be produced economically, retaining an overriding royalty interest for the Partnership.

Abandonment Expenditures

        In 2006, PNR exhausted the $348,066 cash reserve established as of December 31, 2005. In the third quarter of 2006, PNR revised their estimate of abandonment expenses incurred, but not recouped from the Partnership and expenses yet to be incurred for properties, in which the Partnership has an interest to approximately $1.4 million. This revision was caused by increased work necessary because of damages caused by Hurricane Katrina, and increased day rates for labor due to the high demand for labor following Hurricanes Katrina and Rita. As of September 30, 2009, PNR had spent approximately $1.3 million of the $1.4 million estimate. PNR believes all major abandonment charges have been incurred. On December 18, 2008, PNR informed the Trustee that there is no longer a deficit balance due for abandonment accrual for amounts expended and for projected future abandonment expenses for the properties in which the Trust has an interest.

Production and Price Review

        Production volumes for natural gas increased to 14,300 Mcf in the third quarter of 2009 as compared with 5,662 Mcf in the third quarter of 2008 primarily due to production increases in West Delta 61. The average sales price received for natural gas in the third quarter of 2009 was $3.87 per

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Mcf as compared with $13.85 per Mcf in the third quarter of 2008. Crude oil, condensate and natural gas liquids production volumes decreased to 688 barrels in the third quarter of 2009 as compared to 1,106 barrels in the third quarter of 2008. The average sales price in the third quarter of 2009 for crude oil, condensate and natural gas liquids was $46.34 per barrel as compared to $96.78 per barrel in the third quarter of 2008. Production volumes for natural gas decreased to 23,783 Mcf for the nine months ended September 30, 2009 as compared with 68,492 Mcf in the first nine months of 2008. The average sales price received for natural gas in the nine months ended September 30, 2009 was $4.74 per Mcf as compared with $8.47 per Mcf in the first nine months of 2008. Crude oil, condensate and natural gas liquids production volumes decreased to 3,114 barrels in the nine months ended September 30, 2009 as compared to 4,919 barrels in the first nine months of 2008. The average sales price in the nine months ended September 30, 2009 for crude oil, condensate and natural gas liquids was $47.89 per barrel as compared to $64.30 per barrel in the first nine months of 2008.

Termination of the Trust

        The Trust Indenture provides that the Trust will liquidate if the total amount of cash per year received by the Trust falls below certain levels for each of three successive years. As a result of insufficient production on Royalty Properties nearing the end of their estimated productive lives, Royalty income received by the Trust in 2002, 2003 and 2004 fell below the Termination Threshold prescribed by the Trust Indenture. The Trustee had previously taken steps to begin the process of liquidating the Trust; however, the legal proceedings described herein directly challenged whether the Termination Threshold had in fact been met and thus affected the liquidation process, such that the Trustee initially delayed the sale of the Partnership's oil and gas assets in efforts to investigate and resolve the claims. However, due to the continuation of the litigation for more than four years, the related cost to the Trust, the threat that the properties might soon revert back to the MMS, and the opportunity to realize greater proceeds for the benefit of the Trust estate, the Trustee concluded that a public auction of the Partnership's oil and gas assets was in the best interest of the Trust, and the Court had allowed a public auction of these assets to go forward. The Trustee therefore instructed Pioneer to proceed with a public auction of the Partnership's assets on March 18, 2009, and Pioneer complied; but there were no bids submitted at the auction, in the face of the pending litigation by the Plaintiffs described in Part I, Item I, Financial Statements, Note 2. The Trustee then provided notice of another public auction of the Partnership's oil and gas assets, to be held on August 12, 2009. However, this public auction did not go forward, based on a judgment dated August 6, 2009, in which the Court approved the parties' settlement agreement (as detailed in "—Legal Proceedings" below), but held that there was an outstanding procedural issue that needed to be addressed prior to entry of final judgment. The parties to the settlement agreement therefore decided to postpone the sale of the Partnership's oil and gas assets until the Court entered final judgment resolving all issues in the litigation, which took place on September 14, 2009. In accordance with the final judgment and the settlement agreement, the Trustee instructed Pioneer to proceed with a public auction of the Partnership's assets on November 11, 2009. At the November 11, 2009 auction, the highest bidder for the Partnership's assets in the West Delta 61 Block was Emerald Energy, with a sales price of $700,000. The assets of the Partnership and Pioneer in the Brazos A-39 Block did not receive any bids in the auction. Pioneer is entitled to dispose of the Brazos A-39 Block assets in any manner it sees fit, and the Trustee is currently awaiting Pioneer's determination regarding how it will dispose of these assets and the timing for such dispositions, including potentially electing to plug and abandon the property. Any resulting sales proceeds will be remitted to the Trust as part of the wind-down process. The Trustee, which has no

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authority or discretionary control over the timing of expenditures, production or income on the Royalty Properties, has no control over the occurrence of the Termination Threshold or its consequences.

        The Trust Indenture provides the Trustee a two-year period during which it must sell all of the assets of the Partnership. The Trust Indenture provides that such properties must be sold for cash and not for any other consideration. The sale process will be open to any persons desiring to participate, but, as is customary, access to information and participation may be limited to persons who execute confidentiality agreements regarding information provided by the working interest owners. The Trustee may also require bidders to identify themselves clearly and to represent or evidence sufficient financing in order to participate, as the Trustee expects payment will be required promptly after the close of bidding without any financing conditions. Accordingly, the auction may not be a "public" auction in the sense that it may not be open to anyone who does not satisfy these requirements.

Assets and Liabilities in the Process of Liquidation

        As a result of the triggering of the Termination Threshold effective January 1, 2005, the Trust is in the process of liquidation. After a Final Settlement Agreement was approved and Final Judgment was entered by the Court in the Lawsuit, the Trustee directed Pioneer to sell the Partnership assets (along with the Pioneer Settlement Interests), consistent with the terms contained in the Term Sheet and as approved by the Court, at public auction and any resulting sales proceeds will be remitted to the Trust as part of the wind-down process. See "—Legal Proceedings" below. The below table presents the assets of the Trust at their estimated fair value:

        The net overriding royalty interest in oil and gas properties at September 30, 2009 reflect the Trustee's estimate of value (in the absence of third-party appraisals or evaluations) based on the price received at auction on November 11, 2009.

Legal Proceedings

        On April 11, 2005, MOSH Holding, L.P. ("MOSH") filed an Original Petition in the District Court of Travis County, Texas, 250th Judicial District, against PNRC; PNR (together with PNRC, "Pioneer");

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Woodside Energy (USA), Inc. ("Woodside"); and JPMorgan, as Trustee of the Mesa Offshore Trust (Case No. GN501113) (the "Lawsuit"). The Lawsuit was pending before the 334th Judicial District of Harris Country, Texas (the "Court"). MOSH's Original Petition alleged Pioneer and Woodside are liable for various actions, including (1) a wrongful farmout by Pioneer to Woodside of the Brazos A-39 Lease, (2) a wrongful delay by Pioneer in producing the Brazos A-39 Lease and the Midway #5 well drilled thereon, (3) fraudulent accounting practices by Pioneer, (4) breach of fiduciary duty by Pioneer, (5) aiding and abetting breach of fiduciary duty by Woodside, (6) misapplication of Trust property by Pioneer, (7) conspiracy to misapply fiduciary property by Woodside and Pioneer, (8) common law fraud by Pioneer, (9) gross negligence by Pioneer, and (10) breach of the conveyance agreement by Pioneer. As described below, MOSH later added claims against the Trustee for (1) an accounting, and (2) breach of fiduciary duty. The remedies MOSH sought included (a) reconstruing the Trust Indenture to determine that the Trust is not terminated because there has or should have been production that would have generated revenues to extend the life of the Trust, (b) requiring the Trustee to pursue certain claims, or to allow MOSH to pursue such claims, (c) setting aside any farmouts by Pioneer in which there have been conveyances to an alleged affiliate of Pioneer, (d) the removal of JPMorgan as Trustee, (e) the return or forfeiture of compensation to JPMorgan, (f) monetary damages against Pioneer, Woodside and JPMorgan, and (g) unspecified exemplary damages against all defendants.

        MOSH's Original Petition did not contain any claims against the Trustee, except to enjoin the Trustee from terminating the Trust during the pendency of the Lawsuit. In April 2005, the Trustee entered into an agreement with MOSH whereby the Trustee would not sell the Trust assets without first giving MOSH 60-days written notice. This agreement allowed MOSH time to obtain documents and discovery from Pioneer and Woodside, and allowed the Trustee time to investigate the claims asserted by MOSH against Pioneer and Woodside to determine if they had any merit and, most importantly, whether the claims would benefit the Trust. During the six month period between April and October 2005, the Trustee conducted an independent investigation including: numerous meetings and discussions with the parties; reviewing the relevant documents with the Trustee's counsel; employing independent reservoir engineers to evaluate the reserves in which the Trust has an interest; engaging independent joint venture auditors to examine the accounting records of the operator, Pioneer, relating to revenues and expenses allocated to the Partnership's interests; and obtaining from both MOSH and Pioneer their respective legal analyses of the challenged farmout.

        Throughout 2005, the parties also anticipated that the Midway #5 well on the Brazos A-39 Lease that is the primary subject of the Lawsuit would go into production. Given the discrepancy between the reserves claimed by MOSH and those projected by Pioneer for the Midway #5 well, actual production results would significantly impact the Trustee's assessment of whether the Trust was better off with the cost-free override created by the Pioneer-Woodside farmout, or the prior cost-burdened net profits interest that MOSH seeks to restore through the Lawsuit. Unfortunately, Hurricane Katrina struck the Gulf of Mexico in August 2005 and delayed the commencement of production until 2006.

        Faced with this post-Katrina situation in the fall of 2005, the Trustee urged all the parties to consent to a bifurcated trial of the farmout issue on an expedited basis. The Trustee proposed to MOSH that if the Court determined that the farmout was not valid and that restoring the net profits interest would benefit the Trust, then the Trust would reimburse MOSH's reasonable attorneys' fees, up to $100,000, and the Trustee would allow MOSH's counsel to represent the Trust in prosecuting the damages portion of the case. Conversely, if MOSH were to lose on the expedited determination of the farmout issue, and in the absence of more evidence to support any ancillary claims, then MOSH would dismiss the other claims and would not be reimbursed, and the Trustee would move forward to terminate the Trust.

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        Although the Trustee, Pioneer, and Woodside all agreed to an expedited trial of the farmout issues, MOSH balked. Contrary to the assertions of MOSH and the Intervenor Plaintiffs, the Trustee never agreed that the claims asserted by MOSH against Pioneer and Woodside "had merit"—the Trustee simply stated that the farmout issue might merit immediate adjudication at that time to determine if MOSH was legally correct.

        When MOSH refused to agree to an expedited and bifurcated trial as proposed by the Trustee, the Trustee informed MOSH that the Trustee's investigation of MOSH's allegations beyond the farmout issues failed to convince the Trustee that pursuing those claims and incurring the related legal fees and expenses would benefit the Trust. Moreover, the Trustee informed MOSH that the Trustee's independent joint venture auditors and reservoir engineers had not found any evidence to date to support any of MOSH's damage allegations. Therefore, the Trustee informed MOSH that the Trustee's investigation indicated that the Trust was better off with the post-farmout cost-free overriding royalty interest than the pre-farmout cost-burdened net profits interest, so the funding of MOSH's efforts to set aside the farmout with Trust funds would not be in the best interest of the Trust.

        It was at this point, in November 2005, in the midst of the Trustee's negotiations with MOSH to obtain an agreed resolution of MOSH's claims, that MOSH alleged for the first time that the Trustee had a conflict of interest because of JPMorgan's long-standing lending relationship with Pioneer. Although it is clear under the Trust Indenture, the Texas Trust Act, and relevant case law that JPMorgan is not precluded, by holding the position of Trustee, from pursuing commercial banking activities not involving Trust funds, MOSH amended its petition and asserted claims against the Trustee on November 28, 2005.

        Although it responded that MOSH's claims against the Trustee were meritless, to avoid any further assertion that the Trustee could not impartially evaluate MOSH's claims, on November 30, 2005, JPMorgan announced its intention to resign as Trustee, effective January 31, 2006. On December 13, 2005, the lawsuit was transferred to the 334th Judicial District Court of Harris County, Texas. At a hearing on January 27, 2006 in the Harris County Court, the Court denied MOSH's motion for a temporary injunction to remove JPMorgan as Trustee and appoint a principal of MOSH, Timothy Roberson, as a temporary Trustee. At the Court's suggestion, JPMorgan agreed to continue as Trustee, until such time as a substitute trustee was found that fulfilled the qualifications of Trustee stated in the Trust Indenture. Since that hearing, none of the parties ever identified a willing qualified successor Trustee that was not also a lender under one of Pioneer's credit facilities (which status MOSH contended was an alleged conflict of interest).

        On December 8, 2006, Dagger-Spine Hedgehog Corporation ("Dagger-Spine") filed a petition to intervene in the Lawsuit as a Plaintiff, alleging claims virtually identical to MOSH. Another group of unit holders, led by Keith A. Wiegand, (together with Dagger-Spine, the "Intervenors") also filed on March 9, 2007 a petition to intervene as plaintiffs in the Lawsuit, incorporating and adopting the same claims asserted by MOSH. MOSH and the Intervenors are referred to hereinafter as the "Plaintiffs."

        In 2006, after the Court denied MOSH's attempt to remove JPMorgan as Trustee, the parties pursued formal discovery in the Lawsuit. During this period, the Trustee continued to evaluate the merits of the alleged claims against Pioneer and Woodside. A central allegation by MOSH and the Intervenors was that Pioneer and Woodside delayed the commencement of production from the well drilled pursuant to the Pioneer-Woodside farmout—the Midway #5 well on the Brazos A-39 Lease. However, Woodside and Pioneer witnesses gave sworn testimony in depositions about the commercial

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and technical reasons for the delays in bringing the well on line. The well commenced production in April 2006. After production began, the Trustee instructed its independent petroleum reserve engineers to evaluate how the production results and projected future production from the well might affect the value of the Trust's interests. The Trustee's independent engineers determined that the initial production data from the well did not warrant a material change in prior assessments of the value of the Trust's assets.

        Pioneer subsequently reported to the Trustee that production from the well was suspended in July 2006 due to mercury contamination identified at downstream facilities where the production from the well is commingled with production from other wells. An updated evaluation from the Trustee's independent petroleum reserve engineers estimated that revenues from future production likely would not exceed the costs of drilling and completing the well. This confirmed to the Trustee that, if the Partnership's interest in the underlying lease had remained, or was, a cost-burdened net profits interest, instead of the cost-free overriding royalty interest the Partnership held as a result of the Pioneer-Woodside Farmout, the Partnership would not have received, or would not receive, any payments from this production, and the Trust accordingly would not have received any associated distributions. Further, the production data did not support reserves of the size asserted by the Plaintiffs. The well resumed production in February 2007, but the well was shut in again on April 18, 2007 due to an increase in hydrogen sulfide content coincidental with an increase in water production. Pioneer implemented a hydrogen sulfide contingency plan, which was required and approved by the Minerals Management Service ("MMS"), including the installation of the necessary alarm and safety systems. The well was shut in October 4, 2008 after discovery of corrosion in the production separator on the host platform. A replacement production separator was installed on the host platform. The well was returned to production on March 19, 2009, but was subsequently shut in again on September 1, 2009, and has been off production ever since.

        Given its conclusion that the Trust was better off with the post-farmout override, and hoping to end this expensive litigation and liquidate the Trust per the Trust Indenture, the Trustee reached a conditional settlement on January 26, 2007 with Pioneer and Woodside of the claims asserted by the Plaintiffs against Pioneer and Woodside. The conditional settlement was set forth in the Mutual Release and Settlement Agreement dated as of January 26, 2007 (the "Pioneer/Woodside Settlement Agreement"). The Trustee filed a motion for approval of the Pioneer/Woodside Settlement Agreement with the Court on January 30, 2007. The Trustee believed that the Pioneer/Woodside Settlement Agreement was in the best interest of the unit holders, but the Plaintiffs opposed it, and on June 19, 2007, the Court issued an Order denying the Trustee's motion to approve the Pioneer/Woodside Settlement Agreement.

        In June and July 2007, Pioneer and Woodside filed motions with the Court that argued that the claims against them did not have merit as a matter of law. Pioneer's motion included an argument that the Plaintiffs did not have the legal right to sue Pioneer because the claims belong to the Trust, not the beneficiaries of the Trust. On October 19, 2007, the Trustee offered to assign to the Plaintiffs the Trust's claims against Pioneer and Woodside, but the Plaintiffs rejected that offer. Through their counsel, the Plaintiffs and the Trustee also began negotiating a resolution of the claims pending between them, and on October 26, 2007, the Trustee and the Plaintiffs informed the Court of an agreement in principle to settle.

        On December 3, 2007, the Trustee entered into a Settlement Agreement and Release with the Plaintiffs and additional Trust unit holders (the "Plaintiffs' Settlement Agreement"). Also on

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December 3, 2007, the Trustee and the Plaintiffs filed a Joint Motion for Approval of Settlement Agreement (the "Joint Motion"). In response to the Joint Motion, on December 21, 2007, Pioneer filed cross-claims against the Trustee seeking declaratory and injunctive relief to prevent certain aspects of the proposed settlement between the Trustee and the Plaintiffs. On January 14, 2008, the Trustee filed an answer to Pioneer's cross-claims, in which the Trustee denied the cross-claims in their entirety, stated that they were baseless, and set forth numerous affirmative defenses. On January 22, 2008, the Court issued an Order denying the Joint Motion. As a result, the conditions precedent to the Plaintiffs' Settlement Agreement could not be satisfied, and the Plaintiffs' Settlement Agreement became null and void. In addition to denying the Joint Motion, the Court also considered and denied in the same Order (i) the application by the Plaintiffs for the appointment of a temporary trustee and (ii) Pioneer's application for a temporary restraining order. As a result of the Court's denial of the Joint Motion, and the Court's denial of the Plaintiffs' application for the appointment of a temporary trustee, JPMorgan elected not to resign in order to avoid a vacancy, and continues to serve as Trustee.

        On April 28, 2008, the Court issued a Docket Control Order, setting the trial date for December 8, 2008. On July 3, 2008, the Plaintiffs filed a Third Amended Petition, seeking, among other things, to add claims against the Partnership (though its partners Pioneer and the Trustee) and JPMorgan in an individual capacity. By order dated July 3, 2008, the Court denied Pioneer's pending motions for summary judgment, including Pioneer's challenge to Plaintiffs' standing. Pioneer then filed a petition for writ of mandamus to the Houston Fourteenth Court of Appeals on July 22, 2008, seeking to reverse the trial courts' ruling on standing. On September 25, 2008, the Houston Fourteenth Court of Appeals denied Pioneer's petition for writ of mandamus, and Pioneer filed a petition for writ of mandamus with the Supreme Court of Texas on October 1, 2008. On October 24, 2008, the group of unit holders led by Keith A. Wiegand filed a Motion for Non-Suit Without Prejudice, and the Court granted the motion on October 24, 2008. Thus, all references herein to "Plaintiffs" after the date of October 24, 2008 include only MOSH and Dagger-Spine. At a hearing before the Court on October 31, 2008, the Plaintiffs agreed to postpone the trial again, and the trial was scheduled for April 13, 2009. The Supreme Court of Texas denied Pioneer's petition for writ of mandamus on November 21, 2008.

        By notice dated February 6, 2009, which the Trustee mailed to all unit holders of record on February 10, 2009, the Trustee announced again that the Termination Threshold had been met and that, as a result, it had instructed Pioneer to sell the oil and gas assets of the Partnership at public auction on March 18, 2009. In addition, the Trustee announced that the sale would include all of Pioneer's interests in Brazos Block A-39. On March 3, 9, and 12, respectively, unit holders Gordon Stamper, Robert Miles, and Keith Wiegand—formerly part of the group of Intervenors led by Keith Wiegand (collectively, the "Individual Intervenors")—filed pro se motions with the Court, requesting to intervene in the Lawsuit. At the public auction on March 18, 2009, no bids were submitted for the Partnership assets, in the face of the pending litigation with Plaintiffs. On March 25, 2009, Plaintiffs filed their Fourth Amended Original Petition, Application for Temporary Restraining Order, Temporary Injunction, Show Cause Order, and Permanent Injunction. On April 15, 2009 and May 9, 2009, respectively, unit holders Michael Brown and Benjamin Ginter filed additional interventions (collectively, along with other individuals previously defined as such, the "Individual Intervenors").

        On May 18, 2009, the Trustee, on behalf of the Trust, entered into a Final Settlement Agreement with (1) the Plaintiffs, both in their individual capacities and as claimed representatives of the Trust and/or the unit holders, (2) Pioneer and (3) Woodside. The terms of the Final Settlement Agreement include the following: (a) Pioneer will pay to the Trust $13 million and will sell and contribute to the

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Trust any proceeds from the sale of all of its interests in the Brazos Block A-39 (the "Pioneer Settlement Interests"); (b) Trustee will pay to the Trust $5 million and will release all claims for and forgive repayment of the existing $5 million Demand Promissory Note (the "Credit Facility") provided by JPMorgan, as lender, to the Trust; and (c) Woodside will pay to the Trust $1 million. Notwithstanding certain other releases, the Trustee will be permitted to use the remaining balance available under the Credit Facility and any other Trust income to pay Trust liabilities and expenses as permitted under the Trust Indenture prior to the final distribution of any net settlement proceeds. These liabilities and expenses include any out-of-pocket costs incurred for effecting the sale of assets in the Liquidation Process and for any other fees and expenses relating to the administration of the Trust after April 27, 2009. As provided in the Final Settlement Agreement, each of the parties agreed to release any and all claims against the other parties that are, or could have been, asserted in the Lawsuit, including any claims for reimbursement of attorney's fees or costs, except as provided for under the Final Settlement Agreement.

        On June 15, 2009, a group of unit holders, most of whom were part of the former group led by Keith A. Wiegand that had previously voluntarily non-suited their claims, submitted a filing to the Court, seeking to delay certain issues from being heard at the June 18, 2009 settlement hearing. This group of unit holders is referred to herein as the "2009 Unit Holders." On June 18, 2009 and July 23, 2009, the Court held evidentiary hearings on the fairness of the Final Settlement Agreement. The purpose of these hearings was for the Court to determine whether the Final Settlement Agreement should be approved as being in the best interests of the Trust and its unit holders/beneficiaries. The Individual Intervenors, 2009 Unit Holders, and all other objectors were afforded the opportunity to participate in the hearings.

        The Court considered all of the papers filed, the evidence presented, and arguments both for and against the Final Settlement Agreement, and, on August 6, 2009, approved the Final Settlement Agreement and denied all objections thereto. In its Findings of Fact and Conclusions of Law With Respect to Final Settlement Agreement ("Findings of Fact and Conclusions of Law"), the Court ruled that all claims that were raised (or that could have been raised) against the defendants in the Lawsuit were owned by the Trust and/or the Partnership; the Plaintiffs pursued the claims asserted in the Lawsuit on behalf of the Trust and/or the Partnership; the Plaintiffs and the Trustee had the authority to prosecute, resolve, settle and release all released claims on behalf of the Trust, the Partnership and the Plaintiffs; and the settlement was in the best interest of the Trust and its unit holders. The Court also entered findings that full and proper notice of the Lawsuit, the Final Settlement Agreement, and the settlement fairness hearing was provided to all unit holders and that all unit holders were given the opportunity to obtain the related documents and express any objections they may have had regarding the Final Settlement Agreement. The Court considered these unit holder objections in entering the Findings of Fact and Conclusions of Law, and denied all of them.

        The initial judgment by the Court was interlocutory, meaning that it was not yet final, because, while the Court found that all unit holders were fully and properly notified of the Final Settlement Agreement and the related hearing, the Court indicated in its Findings of Fact and Conclusions of Law that it did not appear that the Individual Intervenors were provided notice that the motions to strike their petitions in intervention, filed by Pioneer, would be considered by the Court at the same time as the settlement agreement. Therefore, although the Court denied all of the Individual Intervenors' objections to the settlement, the Court also wanted to consider the related motions to strike their petitions in intervention before entering a final judgment in the Lawsuit.

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        On July 10, 2009, the Trustee mailed a notice to all unit holders of record, announcing that the Termination Threshold had been met and that, in accordance with the Trust Indenture and Final Settlement Agreement, it had instructed Pioneer to sell the oil and gas assets of the Partnership at public auction on August 12, 2009 through The Oil & Gas Asset Clearinghouse, whose website is www.ogclearinghouse.com. However, given the interlocutory nature of the Court's August 6, 2009 judgment, the settling parties agreed to postpone the public auction until after the Court entered final judgment.

        On September 14, 2009, the Court signed its Final Judgment, resolving all parties and all claims in the Lawsuit. This Final Judgment granted the defendants' motion for summary judgment and motion to dismiss claims of Intervenors Keith Wiegand, Robert Miles, Gordon Stamper, Michael Brown, and Benjamin Ginter. Robert Miles non-suited his intervention prior to argument on these motions. The Final Judgment also denied the motion for sanctions filed by Gordon Stamper, and adopted and incorporated the August 6, 2009 Findings of Fact and Conclusions of Law. Thus, there are no longer any issues remaining before the Court, all objections to the Final Settlement Agreement are overruled and denied, all pending petitions in interventions are dismissed, and all related intervenors' claims are dismissed. Additionally, all other claims by parties to the Lawsuit, to the extent not otherwise addressed by the Final Judgment, are dismissed with prejudice. On October 19, 2009, Gordon Stamper filed a petition for writ of mandamus in the Houston Fourteenth Court of Appeals, related to a September 10, 2009 order denying his motion to recuse the Judge presiding over the Lawsuit. The Houston Fourteenth Court of Appeals denied his petition for writ of mandamus in an opinion dated November 3, 2009. Also on November 3, 2009, Gordon Stamper filed a "Motion to Appeal" in the Court, and this Motion has been assigned to the Houston Fourteenth Court of Appeals.

        Given the entry of the Final Judgment, the Trustee directed Pioneer to sell the assets of the Mesa Offshore Royalty Partnership (the "Partnership assets") (along with the Pioneer Settlement Interests), consistent with the terms contained in the Final Settlement Agreement, and as approved by the Court in the Final Judgment, at public auction on November 11, 2009 through The Oil & Gas Asset Clearinghouse, whose website is www.ogclearinghouse.com. Notice of the public auction has been mailed to the unit holders of record at least thirty days before the sale.

        At the public auction, the Partnership assets and the assets contributed to the Trust by Pioneer for sale pursuant to its tender letter of October 10, 2008 (hereafter referred to as "Pioneer Settlement Interests") were offered in two lots: (1) the West Delta 61 Lot; and (2) the Brazos A-39 Lot (together, the "Sales Lots"). There was no right of first refusal as previously considered, and the two lots were offered for sale to the highest bidder(s). The highest bidder for the West Delta 61 Lot was Emerald Energy, with a purchase price of $700,000. The Brazos A-39 Lot, including interests owned by the Partnership and assets contributed to the Trust by Pioneer for sale pursuant to a tender letter, did not receive any bids. Since this liquidation process did not result in the sale of Pioneer's interests in Brazos Block A-39, Pioneer is entitled to dispose of such assets in any manner it sees fit, including by way of example and without limitation, withdrawing from participation in and ownership in Brazos Block A-39 pursuant to the terms of the Offshore Operating Agreement governing this property. In addition, if the Partnership's interests remain unsold and no buyer can be found, Pioneer has the absolute right to cancel and/or extinguish such interests. Until the time of the sale or abandonment of the Partnership's assets, Pioneer, as managing general partner of the Partnership, will continue to operate the Partnership's assets and distribute in the normal course any net proceeds to the Trustee for the benefit of the Trust. The Trustee is currently awaiting Pioneer's determination regarding how it will dispose of

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the Partnership's and Pioneer's interests in the Brazos A-39 Lot and the timing for such dispositions, including potentially electing to plug and abandon the property.

        The Trustee expects to establish a future record date after the West Delta 61 Lot sale and the final sale or abandonment of the interests in the Brazos A-39 Lot, and the concurrent termination of the Trust in accordance with the Trust indenture. This record date will serve as the date for holders of record entitled to final distributions as part of the winding up of the Trust. After such date, the Trustee will not recognize any subsequent transfers of Trust units. The Trustee will also request the termination of trading of Trust units on the OTC Bulletin Board and transfers of beneficial interests by The Depository Trust Company (DTC) for its participants on or prior to such final record date.

        Under the terms of the Final Settlement Agreement, payment of the settlement proceeds by Pioneer, JPMorgan and Woodside into escrow will occur within seven business days after the date of the public auction. The settlement proceeds will be placed into separate, interest-bearing, escrow accounts at JPMorgan and will not be distributed by the Trustee until the Final Judgment becomes final and non-appealable. Should the Final Judgment be reversed, the settlement proceeds will be returned to the respective defendants.

        The final distribution by the Trust of the proceeds (i.e., the settlement proceeds plus any sales proceeds from the public auction of the Partnership assets and the Pioneer Settlement Interests) to Trust unit holders will be made only after the settlement proceeds have been remitted to the Trustee, and the Trustee has deducted any costs incurred for effecting the sale of assets in the liquidation process and any other fees and expenses relating to the administration of the Trust after April 27, 2009. Also, in accordance with the Final Judgment, counsel for the Plaintiffs have been awarded attorney's fees and expenses of $7,750,000, which will be paid and deducted before final distribution. Accordingly, the final distribution of net settlement and sales proceeds by the Trust to its 71,980,216 outstanding units of beneficial interest may be materially less than the gross settlement and sales proceeds.

        The Trustee has made the full detail of the underlying data of the December 31, 2008 reserve report available for use in connection with the sale of the Partnership's Royalty Properties as part of the Trust liquidation. For more information regarding the estimated remaining life of each of the Royalty Properties, the estimated future net revenues of the Royalty Properties and information relating to farm-outs of interests on the Royalty Properties, see Item 1A. "Risk Factors" of the Form 10-K for the year ended December 31, 2008 and Note 8 in the Notes to Financial Statements included elsewhere in the Form 10-K. The final distribution to unit holders will be an amount net of funds required to satisfy all Trust liabilities.

Liquidity and Capital Resources

        In accordance with the provisions of the Trust conveyance, generally all revenues received by the Trust, net of Trust administrative expenses and any cash reserves established for the payment of contingent or future obligations of the Trust, are distributed currently to the unit holders. Based on the current general and administrative expenditures being incurred in connection with the litigation and the absence of Royalty income, the Trustee was required to borrow money in accordance with the Trust Indenture to fund Trust expenses. On September 28, 2007 the Trust entered into a Demand Promissory Note agreement with JPMorgan in order to cover portions of its operating expenses. The lender approved an uncommitted line of credit to the Trust in a principal amount not to exceed $3 million. As part of that agreement, JPMorgan pays the expenses on behalf of the Trust. JPMorgan may decline to

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fund any request of the Trust for borrowings at anytime, for any reason, including the event that JPMorgan has reason to believe that the Trust will not be able to satisfy its obligation to repay the Demand Loans. Interest on the note is calculated at a rate per annum equal to Prime Rate plus two percent (2%), paid annually. The Demand Promissory Note is secured by a pledge of the Trust Estate, as that term is defined in the Trust Indenture, including without limitation the 99.99% general partnership interest in the Mesa Offshore Royalty Partnership owned by the Trust, pursuant to a Pledge Agreement dated September 29, 2007, as amended by the First Amendment to Pledge Agreement dated as of December 3, 2007, executed by the Trust for the benefit of the Lender. The Trust may borrow amounts under this Note until such time as JPMorgan makes demand for payment in full or December 31, 2008, whichever is earlier.

        On December, 3, 2007, JPMorgan, individually and as lender, entered into an Amended and Restated Promissory Note with the Trust as borrower, to amend the Demand Promissory Note to provide for, among other provisions, an extension of the stated maturity date of the Loans made pursuant to the Demand Promissory Note and the Amended and Restated Note until the earlier of (1) December 31, 2009, (2) 31 days after the Trust's receipt of any settlement proceeds, recovery or judgment in connection with the Lawsuit, (3) final liquidation of the Trust's assets, or (4) the Plaintiffs' Settlement Agreement is not approved by the Court. Additionally, the amendment provided that the Trust may continue to obtain loans under the note until the maturity date, as long as the amount borrowed does not exceed $3 million and the loan is not in default. The amendment also provided that interest expense shall be due and payable on the maturity date. On August 25, 2008, the Trustee executed an amended and restated Demand Note that among other things increased the aggregate principal amount available for borrowing to $4 million and amended the definition of "Maturity Date" to delete the text relating to the failure of the Court to approve the Plaintiffs' Settlement Agreement in the Lawsuit.

        On January 28, 2009, the Trustee executed and delivered to JPMorgan a Third Amended and Restated Promissory Note, dated as of January 12, 2009, increasing the principal amount available for the borrowing, subject to the terms of such note, to $5 million.

        As of September 30, 2009, there was outstanding $5,260,198 of principal advanced by JPMorgan, including $5.0 million under the Demand Promissory Note, for payment of Trust expenses together with $410,676 of accrued and unpaid interest expense. At September 30, 2009, the Trust had $0 available under this facility, but $382,741 in trust expenses payable. No assurance can be given that the Trustee will be able to borrow money on terms the Trustee considers reasonable or at all. The Trust intends to pay existing unpaid expenses and future expenses in excess of royalty income through the use of proceeds received from the Final Settlement Agreement or from the sale of the Trust's assets. See "—Legal Proceedings" above.

        The Trust's source of cash is the Royalty income received from the Partnership's share of the net proceeds from the Royalty Properties. Reference is made to Note 8 in the Notes to Financial Statement included in the Form 10-K for the year ended December 31, 2008.

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Item 3.    Quantitative and Qualitative Disclosures About Market Risk.

        The Trust does not engage in any operations, and does not utilize market risk sensitive instruments, either for trading purposes or for other than trading purposes. The Trust's monthly distributions are highly dependent upon the prices realized from the sale of natural gas. Natural gas prices can fluctuate widely on a month-to-month basis in response to a variety of factors that are beyond the control of the Trust and the working interest owners. Factors that contribute to price fluctuation include, among others:

•

political conditions worldwide, in particular political disruption, war or other armed conflict in or affecting oil producing regions;



•

worldwide economic conditions;



•

weather conditions, including hurricanes and tropical storms in the Gulf of Mexico;



•

the supply and price of foreign natural gas;



•

the level of consumer demand;



•

the price and availability of alternative fuels;



•

the proximity to, and capacity of, transportation facilities; and



•

the effect of worldwide energy conservation measures.

Moreover, government regulations, such as regulation of natural gas transportation and price controls, can affect product prices in the long term. See also the discussion of marketing by Pioneer discussed in Item 2. "Management's Discussion and Analysis of Financial Condition and Results of Operations—Operational Review."

Item 4.    Controls and Procedures.

        Evaluation of Disclosure Controls and Procedures.    The Trustee maintains disclosure controls and procedures designed to ensure that information required to be disclosed by the Trust in the reports that it files or submits under the Exchange Act of 1934, as amended, is recorded, processed, summarized and reported within the time periods specified in the SEC's rules and regulations. Disclosure controls and procedures include controls and procedures designed to ensure that information required to be disclosed by the Trust is accumulated and communicated by PNR, as the managing general partner of the Partnership, the working interest owners JPMorgan, as Trustee of the Trust, and its employees who participate in the preparation of the Trust's periodic reports as appropriate to allow timely decisions regarding required disclosure.

        As of the end of the period covered by this report, the trust officer acting on behalf of the Trustee responsible for the administration of the Trust conducted an evaluation of the Trust's disclosure controls and procedures. The officer acting on behalf of the Trustee concluded that the Trust's controls and procedures are effective.

        Due to the contractual arrangements of (i) the Trust Indenture, (ii) the Partnership Agreement and (iii) the rights of the Partnership under the Conveyance regarding information furnished by the working interest owners, the Trustee relies on: (A) information provided by the working interest owners, including (i) the status of litigation, (ii) historical operating data, plans for future operating and

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capital expenditures, reserve information, as well as (iii) information relating to projected production; (B) information provided by the managing general partner of the Partnership that is collected by the managing general partner from the working interest owners; and (C) conclusions regarding reserves by reserve engineers or other experts in good faith. See Item 1A. Risk Factors "—None of the Trust nor its unit holders control the operation or development of the Royalty Properties and have little influence over operation or development" and "—The Trustee relies upon the working interest owners and managing general partner for information regarding the Royalty Properties" in the Trust's Annual Report on Form 10-K for the year ended 2008 for a description of certain risks relating to these arrangements and reliance.

        Changes in Internal Control over Financial Reporting.    In connection with the evaluation by the Trustee of changes in internal control over financial reporting of the Trust that occurred during the Trust's last fiscal quarter, no change in the Trust's internal control over financial reporting was identified that has materially affected, or is reasonably likely to materially affect, the Trust's internal control over financial reporting. The Trustee notes for purposes of clarification that it has no authority over, has not evaluated and makes no statement concerning, the internal control over financial reporting of the working interest owners or the managing general partner of the Partnership.

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PART II

Item 1.    Legal Proceedings.

        See Part I, Item 1, Financial Statements, Note 2, which is incorporated herein by reference. Additional information about our legal proceedings can be found in Part I, Item 3 of our 2008 Annual Report on Form 10-K.

Item 1A.    Risk Factors

        In addition to the other information set forth in this report, including the additional risk factor set forth below, you should carefully consider the factors discussed in "Part I—Item 1A. Risk Factors" in our Annual Report on Form 10-K for the fiscal year ended December 31, 2008, which summarize the principal risks associated with an investment in units in the Trust. The risks described in our Annual Report on Form 10-K are not the only risks associated with an investment in units in the Trust. Additional risks and uncertainties not currently known to us or that we currently deem to be immaterial also may have a material adverse effect on any investment in units in the Trust.

The Royalty will be sold and the Trust terminated.

        In accordance with the Trust Indenture and pursuant to the Final Settlement Agreement, the Trustee will cause the Partnership to sell the Royalty and the Trust will be liquidated. The receipt of settlement proceeds and forgiveness of repayment of certain indebtedness under a promissory note pursuant to the terms of the settlement, the sale of the Royalty and the termination of the Trust will be taxable events to the unitholders. Each unitholder should consult his own tax advisor regarding Trust tax compliance matters, including federal and state tax implications concerning the settlement, the disposition of the Partnership's assets and the termination of the Trust.

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Item 6.    Exhibits.

        (Asterisk indicates exhibit previously filed with the Securities and Exchange Commission and incorporated herein by reference. JPMorgan was formerly known as The Chase Manhattan Bank and is successor by mergers to the original name of the Trustee, Texas Commerce Bank National Association).

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SIGNATURES

        Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

        The Registrant, Mesa Offshore Trust, has no principal executive officer, principal financial officer, board of directors or persons performing similar functions. Accordingly, no additional signatures are available and none have been provided.

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QuickLinks

PART I—FINANCIAL INFORMATION

Item 1. Financial Statements.

MESA OFFSHORE TRUST STATEMENTS OF DISTRIBUTABLE INCOME (Unaudited)
STATEMENT OF ASSETS, LIABILITIES AND TRUST CORPUS
MESA OFFSHORE TRUST STATEMENTS OF CHANGES IN TRUST CORPUS (Unaudited)
MESA OFFSHORE TRUST NOTES TO FINANCIAL STATEMENTS (Unaudited)

Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations.

Item 3. Quantitative and Qualitative Disclosures About Market Risk.
Item 4. Controls and Procedures.

PART II

Item 1. Legal Proceedings.
Item 1A. Risk Factors
Item 6. Exhibits.

SIGNATURES