UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 5, 2012

PLAINS EXPLORATION & PRODUCTION COMPANY

(Exact name of registrant as specified in charter)

Registrant’s telephone number, including area code: (713) 579-6000

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

x Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 7.01 Regulation FD Disclosure.

On December 5, 2012, Plains Exploration & Production Company (“PXP”) and Freeport-McMoRan Copper & Gold Inc. (“FCX”) issued a joint press release announcing that PXP, FCX and IMONC LLC, a wholly owned subsidiary of FCX, entered into a definitive Agreement and Plan of Merger (the “Merger Agreement”) pursuant to which FCX will acquire PXP for approximately $6.9 billion in cash and stock. Under the terms of the Merger Agreement, which has been approved by the boards of directors of both companies, PXP stockholders have the right to elect to receive, for each share of PXP common stock they own, 0.6531 shares of FCX common stock and $25.00 in cash, equivalent to total consideration of $50.00 per PXP share, based on the closing price of FCX stock on December 4, 2012. PXP stockholders may elect to receive cash or stock consideration, subject to proration in the event of oversubscription, with the value of the cash and stock per-share consideration to be equalized at closing.

The press release is attached hereto as Exhibit 99.1 and is incorporated into this Item 7.01 by reference. The information on Exhibit 99.1 shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be incorporated by reference into any filing under the Securities Act of 1933, as amended.

Item 8.01 Other Events.

To the extent required, the information included in Item 7.01 of this Current Report on Form 8-K is incorporated into this item 8.01.

Item 9.01 Financial Statements and Exhibits

IMPORTANT ADDITIONAL INFORMATION WILL BE FILED WITH THE SEC

In connection with the proposed business combination transaction between PXP and FCX, FCX plans to file with the SEC a registration statement on Form S-4 that will contain a proxy statement/prospectus to be mailed to the PXP stockholders in connection with the proposed transaction. THE REGISTRATION STATEMENT AND THE PROXY STATEMENT/PROSPECTUS WILL CONTAIN IMPORTANT INFORMATION ABOUT PXP, FCX, THE PROPOSED TRANSACTION AND RELATED MATTERS. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT AND THE PROXY STATEMENT/PROSPECTUS CAREFULLY WHEN THEY BECOME AVAILABLE. Investors and security holders will be able to obtain free copies of the registration statement and the proxy statement/prospectus and other documents filed with the SEC by PXP and FCX through the web site maintained by the SEC at www.sec.gov. In addition, investors and security holders will be able to obtain free copies of the registration statement and the proxy statement/prospectus by phone, e-mail or written request by contacting the investor relations department of PXP or FCX at the following:

PARTICIPANTS IN THE SOLICITATION

PXP and FCX, and their respective directors and executive officers, may be deemed to be participants in the solicitation of proxies in respect of the proposed transactions contemplated by the Merger Agreement. Information regarding directors and executive officers of PXP is contained in PXP’s definitive proxy statement dated April 13, 2012, which is filed with the SEC. Information regarding FCX’s directors and executive officers is contained in FCX’s definitive proxy statement dated April 27, 2012, which is filed with the SEC. A more complete description will be available in the registration statement and the proxy statement/prospectus.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

Statements in this Current Report on Form 8-K regarding the proposed transaction between PXP and FCX, the expected timetable for completing the proposed transaction, future financial and operating results, benefits and synergies of the proposed transaction, future opportunities for the combined company, and any other statements about PXP or FCX managements’ future expectations, beliefs, goals, plans or prospects constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Any statements that are not statements of historical fact (including statements containing the words “believes,” “plans,” “anticipates,” “expects,” “estimates” and similar expressions) should also be considered to be forward-looking statements. These statements are not guarantees of future performance, and there are a number of important factors that could cause actual results or events to differ materially from those indicated by such forward-looking statements, including: the ability to consummate the proposed transaction; the ability to obtain the requisite regulatory approvals and satisfaction of the other conditions to consummation of the transaction; the ability to realize anticipated benefits and synergies; the potential impact of announcement of the transaction or consummation of the transaction on relationships, including with employees, suppliers, customers and competitors; national, international, regional and local economic, competitive and regulatory conditions and developments; capital and credit markets conditions; the political and economic stability of oil producing nations; energy markets, including changes in the price of certain commodities; environmental conditions; business and regulatory or legal decisions; terrorism; and the other factors described in the Annual Reports on Form 10-K for the year ended December 31, 2011 and other reports filed with the SEC by PXP and FCX. PXP and FCX disclaim any intention or obligation to update any forward-looking statements as a result of developments occurring after the date of this Current Report.

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 hereunto duly authorized.

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