SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

¨ Definitive Additional Materials

x  Soliciting Material under Rule 14a-12

PLAINS RESOURCES INC.

(Name of Registrant as Specified in Its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check the appropriate box):

x  No fee required.

¨ Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

(1)  Title of each class of securities to which transaction applies:

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(3)  Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 11 (set forth the amount on which the filing fee is calculated and state how it was determined):

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¨ Fee paid previously with preliminary materials.

¨ Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the form or schedule and the date of its filing.

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On May 7, 2004 Plains Resources Inc. issued the following press release:

NEWS RELEASE

FOR IMMEDIATE RELEASE

PLAINS RESOURCES SPECIAL COMMITTEE RESPONDS TO LEUCADIA

MARCH 19TH PROPOSAL

HOUSTON, May 7, 2004 – Plains Resources Inc. (NYSE:PLX) announced today that the Special Committee of the Board of Directors of Plains Resources Inc. (“Plains Resources”), which was appointed to consider offers for Plains Resources, has received correspondence from Leucadia National Corporation (“Leucadia”) dated April 30, 2004 (the “April 30th Letter”). The April 30th Letter announced that Moody’s Investors Service has assigned a B2 rating to the debt securities proposed to be issued by Plains Resources under Leucadia’s March 19, 2004 proposal (the “March 19th Proposal”).

The transaction described in the March 19th Proposal, and more fully explained in Leucadia’s press release of the same date, contemplates that Plains Resources stockholders would receive a combination of cash, preferred stock, and debt securities to be issued by Plains Resources. After consideration of the rating by Moody’s, among other things, in its evaluation of the March 19th Proposal, the Special Committee, following review with its financial and legal advisors, has determined in good faith that the March 19th Proposal is reasonably likely to result in a Superior Proposal (as defined in the Vulcan merger agreement described below).

Accordingly, the Special Committee has determined to enter into negotiations with Leucadia regarding the March 19th Proposal, and has requested additional information from Leucadia, including detailed terms of both the proposed debt securities and the proposed preferred stock.

As previously announced, Plains Resources has entered into a merger agreement with an affiliate of Vulcan Capital. Under the terms of the merger agreement, stockholders of Plains Resources, other than James C. Flores and John T. Raymond, would receive $16.75 per share in cash for each share of Plains Resources stock that they own. Plains Resources’ Chairman James C. Flores and its CEO John T. Raymond are participating with the affiliate of Vulcan Capital in the transaction.

PLAINS RESOURCES HAS FILED A PRELIMINARY PROXY STATEMENT FOR THE SPECIAL MEETING OF STOCKHOLDERS TO VOTE ON THE PROPOSED TRANSACTION WITH THE VULCAN GROUP, AND PLAINS RESOURCES AND THE VULCAN GROUP HAVE FILED A SCHEDULE 13E-3 AND MAY FILE OTHER

RELEVANT DOCUMENTS, WITH THE SEC CONCERNING THE PROPOSED TRANSACTION. STOCKHOLDERS ARE URGED TO READ THE PRELIMINARY PROXY STATEMENT AND SCHEDULE 13E-3, WHICH ARE AVAILABLE NOW, AND THE DEFINITIVE PROXY STATEMENT WHEN IT BECOMES AVAILABLE AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC BECAUSE THEY CONTAIN AND WILL CONTAIN IMPORTANT INFORMATION ABOUT THE MERGER AND THE INTERESTS OF THE PARTICIPANTS IN THE SOLICITATION OF PROXIES.

YOU MAY OBTAIN THE DOCUMENTS FREE OF CHARGE AT THE WEBSITE MAINTAINED BY THE SEC AT WWW.SEC.GOV. IN ADDITION, YOU MAY OBTAIN DOCUMENTS FILED WITH THE SEC BY PLAINS RESOURCES FREE OF CHARGE BY REQUESTING THEM IN WRITING FROM PLX AT 700 MILAM, SUITE 3100, HOUSTON, TEXAS 77002, ATTENTION: JOANNA PANKEY, OR BY TELEPHONE AT 832-239-6000.

Plains Resources, James C. Flores, John T. Raymond, Paul G. Allen and the affiliate of Vulcan Capital (which together with Mr. Flores, Mr. Raymond and Mr. Allen form the “Vulcan Group”), and the directors and executive officers of Plains Resources and the affiliate of Vulcan Capital, may be deemed to be participants in the solicitation of proxies from stockholders of Plains Resources in connection with the merger. INFORMATION ABOUT THE DIRECT AND INDIRECT INTERESTS, BY SECURITY HOLDINGS OR OTHERWISE, OF THESE PERSONS IS SET FORTH IN THE COMPANY’S PROXY STATEMENT FOR ITS 2003 ANNUAL MEETING, THE SCHEDULE 13D FILED WITH THE SEC BY THE VULCAN GROUP ON DECEMBER 1, 2003, AS SUBSEQUENTLY AMENDED, AND THE PRELIMINARY PROXY STATEMENT FOR THE SPECIAL MEETING OF STOCKHOLDERS FILED WITH THE SEC AND THE SCHEDULE 13E-3 FILED WITH THE SEC. SUCH INFORMATION WILL ALSO BE CONTAINED IN THE DEFINITIVE PROXY STATEMENT TO BE FILED WITH THE SEC.

About Plains

Plains Resources is an independent energy company engaged in the acquisition, development and exploitation of crude oil and natural gas. Through its ownership in Plains All American Pipeline, L.P., Plains Resources has interests in the midstream activities of marketing, gathering, transportation, terminalling and storage of crude oil. Plains Resources is headquartered in Houston, Texas.

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