UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D. C. 20549

FORM 10-K/A

þ     ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2009

OR

¨     TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Commission file number: 001-31470

PLAINS EXPLORATION & PRODUCTION COMPANY

(Exact name of registrant as specified in its charter)

700 Milam Street, Suite 3100

Houston, Texas 77002

(Address of principal executive offices)

(Zip Code)

(713) 579-6000

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: none

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes   ü     No      

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes          No   ü

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   ü     No      

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

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.       ü

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. (Check one):

  ü  Large accelerated filer      Accelerated filer      Non-accelerated filer  (Do not check if a smaller reporting company)      Smaller reporting company

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

The aggregate market value of the Common Stock held by non-affiliates of the registrant (treating all executive officers and directors of the registrant, for this purpose, as if they may be affiliates of the registrant) was approximately $3.3 billion on June 30, 2009 (based on $27.36 per share, the last sale price of the Common Stock as reported on the New York Stock Exchange on such date). On January 29, 2010, there were 139.4 million shares of the registrant’s Common Stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE: The information required in Part III of the Annual Report on Form 10-K is incorporated by reference to the registrant’s definitive proxy statement to be filed pursuant to Regulation 14A for the registrant’s 2010 Annual Meeting of Stockholders.

EXPLANATORY NOTE

Plains Exploration & Production Company, or PXP, is filing this Amendment No. 1 to our Form 10-K for the year ended December 31, 2009 originally filed with the Securities and Exchange Commission on February 25, 2010, or the 2009 Form 10-K, solely for the purpose of filing revised reports from one of our third-party petroleum engineering firms. The reports from Ryder Scott Company, L.P., or Ryder Scott, were filed as Exhibit 99.3 and 99.4 to the 2009 Form 10-K. In addition to the revised reports being filed as Exhibit 99.3 and 99.4, we are including in this Form 10-K/A a consent from Ryder Scott in Exhibit 23.3 and certifications of our principal executive officer and principal financial officer in Exhibit 31.1 and 31.2.

No item of or disclosures appearing in our 2009 Form 10-K are affected by this filing other than the exhibits described above. This report on Form 10-K/A is presented as of the filing date of the 2009 Form 10-K and does not reflect events occurring after that date, or modify or update disclosures in any way.

PART IV

Item 15. Exhibits, Financial Statement Schedules

(a) (3) Exhibits

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) 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.

EXHIBIT INDEX