Exhibit 99.3

UNAUDITED PRO FORMA FINANCIAL INFORMATION

On September 4, 2013, Gastar Exploration USA, Inc. (“Gastar USA”), a subsidiary of Gastar Exploration Ltd. (the “Company”), entered into a Purchase and Sale Agreement, dated September 4, 2013, by and among Lime Rock Resources II-A, L.P. and Lime Rock Resources II-C, L.P, (together, the “Lime Rock Parties”) and Gastar USA (the “WEHLU Purchase Agreement”). Pursuant to the WEHLU Purchase Agreement, Gastar USA will acquire a 98.3% working interest (80.5% net revenue interest) in 24,000 net acres of the West Edmond Hunton Lime Unit (“WEHLU”) located in Kingfisher, Logan and Oklahoma Counties, Oklahoma, for a cash purchase price of $187.5 million, subject to, among other customary adjustments, adjustment for an acquisition effective date of August 1, 2013 (the “WEHLU Acquisition”).

The closing of the WEHLU Acquisition is subject to satisfaction of customary closing conditions and delivery of the total acquisition purchase price. The transaction is expected to be funded from a combination of net proceeds from the issuance of 10.75% perpetual preferred stock by Gastar USA, cash on hand, borrowings under Gastar USA’s senior revolving credit facility or from a possible offering of senior notes. This pro forma information was prepared assuming that the purchase price for the pending WEHLU Acquisition will be funded from pro forma cash on hand and net proceeds from the issuance of perpetual preferred stock by Gastar USA, which the Company and Gastar USA have assumed will be at a dividend rate of 10.75% and issued in the aggregate stated value of $100.0 million for purposes of the following unaudited pro forma financial information. The actual sources of funding of the purchase price and amounts from various sources may differ.

Gastar USA currently anticipates the transaction will close in late November 2013. There is no assurance, however, that the WEHLU Acquisition will be completed or that expected benefits of the pending acquisition will be realized. The WEHLU Purchase Agreement may be terminated by either party if the closing has not occurred on or before December 31, 2013.

On October 2, 2013, Gastar Exploration Texas, LP (“Gastar Texas”) and Gastar Exploration USA, Inc. (“Gastar USA”), subsidiaries of Gastar Exploration Ltd. (the “Company” or “Gastar LTD” ), sold to Cubic Energy, Inc. (“Cubic Energy”) approximately 31,800 gross (16,300 net) acres of leasehold interests in the Hilltop area of East Texas in Leon and Robertson Counties, Texas, including production from interests in producing wells, for an adjusted cash purchase price of approximately $43.9 million (the “East Texas Divestiture”).

On June 7, 2013, Gastar USA purchased from Chesapeake Exploration, L.L.C. and Larchmont Resources, L.L.C. approximately 157,000 net acres of Mid-Continent oil and gas leasehold interests, including production from interests in 176 net producing locations in Oklahoma, for approximately $69.4 million (the “Chesapeake Acquisition”). The Chesapeake Acquisition had an effective date of October 1, 2012. In connection with the Chesapeake Acquisition, the Company, Gastar Texas and Gastar Exploration Texas, LLC entered into a Settlement Agreement with Chesapeake Energy Corporation, L.L.C. and Chesapeake Energy Corporation and its affiliates (together, “Chesapeake”). In order to effect a mutual full and unconditional release and settlement of all claims made in a lawsuit filed by Chesapeake, Gastar USA agreed to pay Chesapeake approximately $10.8 million in cash, approximately $9.8 million of which to repurchase 6,781,768 outstanding common shares of the Company’s common stock held by Chesapeake (the “Chesapeake Share Repurchase”). The Chesapeake Share Repurchase was also completed on June 7, 2013. Subsequent to the closing of the Chesapeake Acquisition, on July 1, 2013, Gastar USA’s partner in an original area of mutual interest (“AMI”) in Oklahoma elected to exercise its rights within the AMI and acquired approximately 12,820 net acres and 50% of the interest acquired in 62 producing wells (effective October 1, 2012) previously acquired by Gastar USA as part of the Chesapeake Acquisition for a cash purchase price of $12.1 million (the “AMI Election”). Collectively, these transactions are referred to as the “Hunton Transactions.”

On May 15, 2013, Gastar USA issued $200 million aggregate principal amount of its 8 5/8% Senior Secured Notes due 2018 under an indenture by and among Gastar USA, the Guarantors named therein, and Wells Fargo Bank, National Association, as Trustee and Collateral Agent (the “Notes Offering”). The net proceeds from the offering were used to (i) finance the Chesapeake Acquisition and the Chesapeake Share Repurchase and to settle litigation with Chesapeake, (ii) repay in full borrowings under the prior revolving credit facility and (iii) for general corporate purposes.

On August 6, 2013, (i) Newfield Exploration Mid-Continent Inc. (“Newfield”) acquired approximately 76,000 net acres of undeveloped oil and gas leasehold interests in Kingfisher and Canadian Counties, Oklahoma from Gastar USA, for an adjusted cash purchase price of approximately $54.1 million and (ii) Gastar USA acquired approximately 1,850 net acres of Oklahoma undeveloped oil and gas leasehold interests from Newfield (the “Gastar Acquired Acreage”) through a downward adjustment to the purchase price (collectively, the “Newfield Divestiture”). The Newfield Divestiture had an effective date of May 1, 2013.

1

The following unaudited pro forma financial information is derived from the historical financial statements of the Company and Gastar USA and the audited statements of revenues less direct operating expenses of the assets acquired in the Chesapeake Acquisition and the assets to be acquired in the WHELU Acquisition, and reflect the impact of the WEHLU Acquisition, East Texas Divestiture, the Hunton Transactions and the Newfield Divestiture. The Unaudited Pro Forma Combined Balance Sheet of the Company as of June 30, 2013 and the Unaudited Pro Forma Combined Balance Sheet of Gastar USA as of June 30, 2013 have been prepared assuming the WEHLU Acquisition, East Texas Divestiture, the AMI Election and the Newfield Divestiture were consummated on June 30, 2013. The impact of the Hunton Transactions, except the AMI Election, are already reflected in the historical balance sheets of the Company and Gastar USA at June 30, 2013. The Unaudited Pro Forma Combined Statements of Operations of the Company and Gastar USA for the year ended December 31, 2012 and for the six month period ended June 30, 2013 have been prepared assuming the WEHLU Acquisition, East Texas Divestiture and the Hunton Transactions were consummated on January 1, 2012. The Newfield Divestiture is a disposition of undeveloped oil and gas leasehold interests and is accounted for as an adjustment of capitalized costs, with no gain recognized as such adjustment would not significantly alter the relationship between capitalized costs and proved reserves of oil and gas attributable to the Company’s or Gastar USA’s full cost pool. Therefore, the Newfield Divestiture has no impact on the statement of operations. The probable WEHLU Acquisition is assumed to be financed through the issuance of $100.0 million of a new series of perpetual preferred stock issued by Gastar USA and the utilization of a portion of pro forma cash on hand. The new issue of perpetual preferred stock is assumed to have a dividend rate of 10.75%.

These unaudited pro forma combined financial statements should be read in conjunction with the notes hereto and the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2012, as amended, and the Quarterly Report on Form 10-Q for the three and six months ended June 30, 2013, as well as the Statement of Revenues and Direct Operating Expenses of the Chesapeake Acquisition Properties filed as exhibit 99.1 to the Current Report on Form 8-K/A dated June 27, 2013, as amended by the Current Reports on Form 8-K/A dated October 25, 2013, and the Statement of Revenues and Direct Operating Expenses of the WEHLU Acquisition Properties filed as exhibit 99.1 to this Current Report on Form 8-K, each as jointly filed by the Company and Gastar USA.

The unaudited pro forma financial information is not indicative of the financial position or results of operations of the Company or Gastar USA which would have actually occurred if the transaction had occurred at the dates presented or which may be obtained in the future. In addition, future results may vary significantly from the results reflected in such statements due to normal oil and natural gas production declines, reductions in prices paid for oil or natural gas, future acquisitions or dispositions and other factors.

2

GASTAR EXPLORATION LTD.

UNAUDITED PRO FORMA COMBINED BALANCE SHEET

AS OF JUNE 30, 2013

See accompanying notes to unaudited pro forma combined financial statements.

3

GASTAR EXPLORATION LTD.

UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS

FOR THE SIX MONTHS ENDED JUNE 30, 2013

See accompanying notes to unaudited pro forma combined financial statements.

4

GASTAR EXPLORATION LTD.

UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS

FOR THE YEAR ENDED DECEMBER 31, 2012

See accompanying notes to unaudited pro forma combined financial statements.

5

GASTAR EXPLORATION USA, INC.

UNAUDITED PRO FORMA COMBINED BALANCE SHEET

AS OF JUNE 30, 2013

See accompanying notes to unaudited pro forma combined financial statements.

6

GASTAR EXPLORATION USA, INC.

UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS

FOR THE SIX MONTHS ENDED JUNE 30, 2013