<PAGE>
 
     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON MAY 28, 1997
 
                                                    Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    --------
                                    FORM S-8
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                                    --------
                             PLAINS RESOURCES INC.
             (Exact name of registrant as specified in its charter)

        DELAWARE                                        13-2898764
(State or other jurisdiction of             (I.R.S. Employer Identification No.)
incorporation or organization)

                               1600 SMITH STREET
                              HOUSTON, TEXAS 77002
                                 (713) 654-1414
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)
                                   --------

               PLAINS RESOURCES INC. 1996 PERFORMANCE OPTION PLAN
                            (full title of the plan)


                              MICHAEL R. PATTERSON
                       VICE PRESIDENT AND GENERAL COUNSEL
                             PLAINS RESOURCES INC.
                               1600 SMITH STREET
                              HOUSTON, TEXAS 77002
                                 (713) 654-1414
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                                   --------
                                        
                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION> 
========================================================================================================
                                                             PROPOSED         PROPOSED                 
                                                             MAXIMUM          MAXIMUM                      
                                            AMOUNT TO     OFFERING PRICE     AGGREGATE        AMOUNT OF
TITLE OF EACH CLASS OF                    BE REGISTERED     PER SHARE      OFFERING PRICE   REGISTRATION 
SECURITIES TO BE REGISTERED                    (1)            (2)              (2)               FEE 
-------------------------------------------------------------------------------------------------------- 
<S>                                      <C>              <C>              <C>              <C>
Common Stock, par value $.10 per share   500,000 shares      $14.44         $7,220,000       $2,187.88
========================================================================================================
</TABLE>
(1) The amount to be registered also includes such indeterminant number of
    shares of Common Stock as may be issued by reason of the anti-dilution
    provisions of the 1996 Performance Option Plan.

(2) Pursuant to Rule 457(h), the proposed maximum offering price is estimated,
    solely for the purpose of determining the registration fee, on the basis of
    the average high and low sales prices of the Common Stock as reported by the
    American Stock Exchange on May 22, 1997, which was $14.44.

================================================================================
<PAGE>
 
                                    PART II
                                        
              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT
                                        

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

     Plains Resources Inc., a Delaware corporation (the "Company") hereby
incorporates by reference in this Registration Statement the following
documents:

     (a) The Company's Annual Report on Form 10-K for the fiscal year ended
December 31, 1996.

     (b) All other reports filed pursuant to Section 13(a) or 15(d) of the
Securities Act of 1934, as amended, (the "Exchange Act"), since the fiscal year
ended December 31, 1996.

     (c) The description of the Company's common stock, $0.10 par value (the
"Common Stock"), contained in a registration statement on Form 8-A filed
pursuant to the Exchange Act, including any amendment or report filed for the
purpose of updating such description.

     All documents subsequently filed by the Company pursuant to Section 13(a),
13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a post-effective
amendment which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, is hereby deemed to be
incorporated by reference in this Registration Statement and a part hereof from
the date of the filing of such documents.


ITEM 4.  DESCRIPTION OF SECURITIES.

     Not applicable.


ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

     The consolidated financial statements incorporated in this Registration
Statement by reference to the  Annual Report on Form 10-K of the Company for the
year ended December 31, 1996, have been so incorporated in reliance on the
reports of Price Waterhouse LLP, independent accountants, given on the authority
of said firm as experts in auditing and accounting.  Information relating to the
estimated quantities of proved reserves of oil and gas and the related estimates
of future net revenues and present values thereof for certain periods, included
in the Company's Annual Report on Form 10-K for the year ended December 31,
1996, as well as in the Notes to the Consolidated Financial Statements of the
Company in such Annual Report, have been prepared by Netherland, Sewell &
Associates, Inc., H. J. Gruy and Associates, Inc., and Ryder Scott Company,
independent petroleum engineers, and are incorporated herein in reliance upon
the authority of said firms as experts in petroleum engineering.   The validity
of the issuance of the shares of Common Stock registered hereby will be passed
upon by Michael R. Patterson, Esq., Vice President and General Counsel of the
Company.  Mr. Patterson beneficially owns 115,603 shares of Common Stock.


ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     Article Eleventh of the Company's Certificate of Incorporation provides
that the Company shall indemnify to the full extent authorized or permitted by
law any person made, or threatened to be made, a party to any action, suit or
proceeding (whether civil, criminal or otherwise) by reason of fact that he, his
testator or intestate, is or was a director or officer of the Company or by
reason of the fact that such director or officer, at the request of the Company,
is or was serving any other corporation, partnership, joint venture, trust,

                                      II-1
<PAGE>
 
employee benefit plan or other enterprise, in any capacity.  The rights to
indemnification set forth above are not exclusive of any other rights to which
such person may be entitled under any statute, provision of the Company's
Certificate of Incorporation or Bylaws, agreements, vote of stockholders or
disinterested directors or otherwise.

     Additionally, Article VIII of the Company's Bylaws provides for mandatory
indemnification to at least the extent specifically allowed by Section 145 of
the General Corporation Law of the State of Delaware (the "GCL").  The Bylaws
generally follow the language of Section 145 of the GCL, but in addition specify
that any director, officer, employee or agent may apply to any court of
competent jurisdiction in the State of Delaware for indemnification to the
extent otherwise permissible under the Bylaws, notwithstanding any contrary
determination denying indemnification made by the Board, by independent legal
counsel, or by the stockholders, and notwithstanding the absence of any
determination with respect to indemnification.  The Bylaws also specify certain
circumstances in which a finding is required that the person seeking
indemnification acted in good faith, for purposes of determining whether
indemnification is available.  Under the Bylaws, a person shall be deemed to
have acted in good faith and in a manner he reasonably believed to be in or not
opposed to the best interests of the Company, or, with respect to any criminal
action or proceeding, to have had no reasonable cause to believe his conduct was
unlawful, if his action is based on the records or books of account of the
Company or another enterprise, or on information supplied to him by the officers
of the Company or another enterprise in the course of their duties, or on the
advise of legal counsel for the Company or another enterprise or on information
or records given or reports made to the Company or another enterprise by an
independent certified public accountant or by an appraiser or other expert
selected with reasonable care by the Company or another enterprise.

     Pursuant to Section 145 of the GCL, the Company generally has the power to
indemnify its current and former directors, officers, employees and agents
against expenses and liabilities incurred by them in connection with any suit to
which they are, or are threatened to be made, a party by reason of their serving
in such positions so long as they acted in good faith and in a manner they
reasonably believed to be in, or not opposed to, the best interests of the
Company, and with respect to any criminal action, they had no reasonable cause
to believe their conduct was unlawful.  With respect to suits by or in the right
of the Company, however, indemnification is generally limited to attorneys' fees
and other expenses and is not available if such person is adjudged to be liable
to the Company unless the court determines that indemnification is appropriate.
The statute expressly provides that the power to indemnify authorized thereby is
not exclusive of any rights granted under any bylaws, agreement, vote of
stockholders or disinterested directors, or otherwise.  The Company also has the
power to purchase and maintain insurance for such persons.

     The above discussion of the Company's Certificate of Incorporation and
Bylaws and Section 145 of the GCL is not intended to be exhaustive and is
qualified in its entirety by each of such documents and such statute.

     The Company has entered into employment agreements containing
indemnification provisions with the following officers; Mr. Greg L. Armstrong,
President and Chief Executive Officer and Mr. William C. Egg, Jr., its Senior
Vice President.  Pursuant to such agreements, the Company has agreed to
indemnify and hold each such officer harmless to the fullest extent permitted by
law, from any loss, damage or liability incurred in the course of his respective
employment.  The amount paid by the Company is reducible by the amount of
insurance paid to or on behalf of such officer with respect to any event giving
rise to indemnification.  Each such officer's right to indemnification is to
survive his respective death or termination of employment and the termination of
his applicable employment agreement.


ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

     Not applicable.

                                      II-2
<PAGE>
 
ITEM 8.  EXHIBITS.

    4.1  Stock Option Agreement dated August 27, 1996, between the Company and
         Greg L. Armstrong (incorporated by reference to Exhibit 10(l) to the
         Company's Annual Report on Form 10-K for the year ended December 31,
         1996).

    4.2  Stock Option Agreement dated August 27,1996, between the Company and
         William C. Egg, Jr. (incorporated by reference to Exhibit 10(m) to the
         Company's Annual Report on Form 10-K for the year ended December 31,
         1996).

    5    Opinion of Michael R. Patterson, Esq. regarding legality of securities
         being registered.

    23.1 Consent of Price Waterhouse, independent accountants.

    23.2 Consent of Netherland, Sewell & Associates, Inc., independent
         petroleum engineers.

    23.3 Consent of H. J. Gruy and Associates, Inc., independent petroleum
         engineers.

    23.4 Consent of Ryder Scott Company, independent petroleum engineers.

    23.5 Consent of Michael R. Patterson, Esq. (contained in Exhibit 5
         hereto).

    24   Power of attorney (contained on page II-5 hereof).


ITEM 9.  UNDERTAKINGS

     The undersigned registrant hereby undertakes:

     (1)  To file during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement:

          (i) To include any prospectus required by Section 10(a)(3) of the
          Securities Act of 1933, as amended (the "Securities Act");

          (ii) To reflect in the prospectus any facts or events arising after
          the effective date of this Registration Statement (or the most recent
          post-effective amendment hereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in this Registration Statement; and

          (iii)  To include any material information with respect to the plan of
          distribution not previously disclosed in this Registration Statement
          or any material change to such information in this Registration
          Statement;

Provided however, that paragraphs (i) and (ii) do not apply if the information
required to be included in a post-effective amendment by those paragraphs is
contained in periodic reports filed by the Company pursuant to Section 13 or
15(d) of the Exchange Act that are incorporated by reference in this
Registration Statement.

     (2) That, for the purpose of determining any liability under the Securities
Act, each such post-effective amendment shall be deemed to be a new registration
statement relating to the securities offered herein, and the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

     (3) To remove from registration by means of a post-effective amendment any
of the securities being registered that remain unsold at the termination of the
offering.

                                      II-3
<PAGE>
 
     The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the Company's
Annual Report pursuant to Section 13(a) or Section 15(d) of the Exchange Act
that is incorporated by reference into this Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
herein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

     Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers, and controlling persons of the Company
pursuant to the foregoing provisions, or otherwise, the Company has been advised
that in the opinion of the Securities and Exchange Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable.  In the event that a claim for indemnification
against such liabilities (other than the payment by the Company of expenses
incurred or paid by a director, officer or controlling person of the Company in
the successful defense of any action, suit proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Company will, unless in the opinion of its counsel, the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question of whether such indemnification by it is against
public policy as expressed in the Securities Act and will be governed by the
final adjudication of such issue.

                                      II-4
<PAGE>
 
                               POWER OF ATTORNEY

   KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Phillip D. Kramer and Michael R. Patterson, and
each of them, either one of whom may act without joinder of the other, his true
and lawful attorneys-in-fact and agents, with full power of substitution and
resubstitution, for him and in his name, place and stead, in any and all
capacities, to sign any or all pre- and post- effective amendments to this
Registration Statement, and to file the same, with all exhibits thereto and
other documents in connection therewith, with the Securities and Exchange
Commission, granting unto said attorneys-in-fact and agents, and each of them,
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in and about the premises, as fully to all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents, and each of them, or the
substitute or substitutes of any or all of them, may lawfully do or cause to be
done by virtue hereof.

                                   SIGNATURES

   Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing a Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Houston, State of Texas, on May 22, 1997.
 
                                        PLAINS RESOURCES INC.
 
 
                                        By: /s/Greg L. Armstrong
                                           ----------------------------------
                                        Greg L. Armstrong
                                        President and Chief Executive Officer


   Pursuant to the requirements of the Securities Act of 1933, this Registration
Statement has been signed by the following persons, in the capacities indicated
on May 22, 1997.


               Signature                            Title
               ---------                            -----


        /s/Greg L. Armstrong               President, Chief Executive
--------------------------------------        Officer and Director
          Greg L. Armstrong               (Principal Executive Officer)

 
        /s/Cynthia A. Feeback               Controller and Principal
--------------------------------------         Accounting Officer
          Cynthia A. Feeback


        /s/Phillip D. Kramer                   Vice President, Chief
--------------------------------------    Financial Officer and Treasurer
            Phillip D. Kramer              (Principal Financial Officer)

                                      II-5
<PAGE>
 
         /s/Jerry L. Dees                             Director
--------------------------------------
            Jerry L. Dees
 

         /s/Tom H. Delimitros                         Director
--------------------------------------                     
          Tom H. Delimitros


       /s/William M. Hitchcock                        Director
--------------------------------------                    
        William M. Hitchcock


          /s/Dan M. Krausse                           Director
--------------------------------------
           Dan M. Krausse


          /s/John H. Lollar                           Director
--------------------------------------
           John H. Lollar


          /s/Robert V. Sinnott                        Director
--------------------------------------
           Robert V. Sinnott


          /s/J. Taft Symonds                          Director
--------------------------------------
           J. Taft Symonds

                                      II-6
<PAGE>
 
                                 EXHIBIT INDEX
                                 -------------


Exhibit
Number      Description of Exhibits
------      -----------------------
 
4.1         Stock Option Agreement dated August 27, 1996, between the Company
            and Greg L. Armstrong (incorporated by reference to Exhibit 10(l) to
            the Company's Annual Report on Form 10-K for the year ended December
            31, 1996).
 
4.2         Stock Option Agreement dated August 27,1996, between the Company
            and William C. Egg, Jr. (incorporated by reference to Exhibit 10(m)
            to the Company's Annual Report on Form 10-K for the year ended
            December 31, 1996).

5           Opinion of Michael R. Patterson, Esq. regarding legality of
            securities being registered.

23.1        Consent of Price Waterhouse, independent accountants.

23.2        Consent of Netherland, Sewell & Associates, Inc., independent
            petroleum engineers.

23.3        Consent of H. J. Gruy and Associates, Inc., independent petroleum
            engineers.

23.4        Consent of Ryder Scott Company, independent petroleum engineers.

23.5        Consent of Michael R. Patterson, Esq. (contained in Exhibit 5
            hereto).

24          Power of attorney (contained on page II-5 hereof)