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                                                                   EXHIBIT 10.10
                                                                  EXECUTION COPY

                         REGISTRATION RIGHTS AGREEMENT

     THIS REGISTRATION RIGHTS AGREEMENT is made as of June 8, 2001 (this
"AGREEMENT"), among Plains Resources Inc., a Delaware corporation (the
"ISSUER"), and EnCap Energy Capital Fund III, L.P. ("FUND III"), EnCap Energy
Capital Fund III-B, L.P. ("FUND III-B"), BOCP Energy Partners, L.P. ("BOCP"),
and Energy Capital Investment Company PLC ("ENCAP PLC" and collectively with
Fund III, Fund III-B, BOCP and EnCap PLC, "ENCAP").  Each EnCap entity and its
permitted transferees shall be referred to herein collectively as the "HOLDERS"
and individually as a "HOLDER."

                              W I T N E S S E T H:

     WHEREAS, EnCap and the Issuer have entered into a Letter Agreement dated as
of June 8, 2001 (the "LETTER AGREEMENT").

     WHEREAS, as an inducement to cause the Conversion (as defined in the Letter
Agreement) the Issuer has agreed to extend to EnCap certain registration rights,
and EnCap and the Issuer desire to enter into this Agreement in connection with
the transactions contemplated by the Letter Agreement.

     NOW, THEREFORE, in consideration of the foregoing and the mutual promises,
representations, warranties, covenants and agreements contained herein, the
parties hereto, intending to be legally bound hereby, agree as follows:

                                   ARTICLE 1
                                  DEFINITIONS

SECTION 1.1    DEFINITIONS.  As used in this Agreement, the following terms
shall have the following respective meanings:

          "AFFILIATE" means, with respect to any specified Person, any other
Person that directly, or indirectly through one or more intermediaries,
controls, is controlled by, or is under common control with, such specified
Person.

          "BOARD" means the Issuer's board of directors.

          "COMMISSION" shall mean the Securities and Exchange Commission or any
successor governmental body or agency.

          "COMMON STOCK" means common stock, par value $0.10 per share, of the
Issuer.

          "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
amended.

          "FORM S-3" means such form under the Securities Act as in effect on
the date hereof or any successor registration form under the Securities Act
subsequently adopted by the
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Commission which permits inclusion or incorporation of substantial information
by reference to other documents filed by the Issuer with the Commission.

          "LOSS" shall have the meaning ascribed thereto in Section 2.6(a).

          "PERSON" shall mean any natural person, firm, individual, business
trust, association, corporation, partnership, joint venture, company, limited
liability company, unincorporated entity or other entity.

          "REGISTRABLE SECURITIES" shall mean Common Stock issued upon
conversion of the Series F Stock and the Series H Stock beneficially owned by
any Holder, including, without limitation, any stock or other securities into
which or for which such Common Stock may hereafter be changed, converted or
exchanged and any other stock or securities issued to Holders of such Common
Stock (or such stock or other securities into which or for which such stock is
so changed, converted or exchanged) upon any reclassification, combination,
subdivision, dividend, exchange, merger, consolidation or similar transaction or
event.  Notwithstanding the foregoing, as to any particular Registrable
Securities, such Registrable Securities shall cease to be Registrable Securities
as soon as (i) such Registrable Securities have been sold or otherwise disposed
of pursuant to a registration statement that was filed with the Commission in
accordance with this Agreement and declared effective under the Securities Act,
(ii) such Registrable Securities shall have been otherwise sold, transferred or
disposed of by a Holder to any Person that is not a Holder, (iii) such
Registrable Securities have been sold in a transaction exempt from the
Securities Act under Section 4(1) thereof so that all transfer restrictions and
restrictive legends with respect thereto are removed upon the consummation of
such sale, (iv) such Registrable Securities are in the opinion of counsel
reasonably acceptable to Holder able to be sold pursuant to Rule 144(k); or (v)
such Registrable Securities are held by a Holder that does not "beneficially
own" more than 1% of the outstanding Common Stock and such Common Stock is able
to be sold under Rule 144 (other than Rule 144(k)).

          "REGISTRATION EXPENSES" shall mean any and all expenses incident to
performance of or compliance with any registration of securities pursuant to
Article 2, including, without limitation, (i) all expenses, including filing
fees, in connection with the preparation, printing and filing of one or more
registration statements hereunder; (ii) the fees, disbursements and expenses of
the Issuer's counsel and accountants (including in connection with the delivery
of opinions and/or comfort letters) in connection with this Agreement and the
performance of the Issuer's obligations hereunder; (iii) the reasonable fees,
disbursements and expenses of one counsel for the Selling Holders (not to exceed
$15,000 for any one registration) selected by them with the approval of the
Issuer (which shall not be unreasonably withheld); (iv) the cost of printing or
producing any agreements among underwriters, underwriting agreements, and blue
sky or legal investment memoranda (which shall not include legal fees of the
underwriters); (v) the filing fees incident to securing any required review by
the National Association of Securities Dealers, Inc. of the terms of the sale of
the securities to be disposed of; (vi) fees and expenses of other Persons
reasonably necessary in connection with such offering, including experts,
transfer agents and registrars; (vii) all security engraving and security
printing expenses; and (viii) all fees and expenses payable in connection with
the listing of the Registrable Securities on any securities exchange or
automated interdealer quotation system on which the Registrable Securities are
then
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listed; provided that Registration Expenses shall exclude all underwriting
discounts, selling commissions and transfer taxes, if any, in connection with
the sale of any Registrable Securities.

          "RULE 144" shall mean Rule 144 (or any successor rule to similar
effect) promulgated under the Securities Act.

          "SECURITIES ACT" shall mean the Securities Act of 1933, as amended.

          "SELLING HOLDER" shall mean any Holder who sells Registrable
Securities pursuant to a registration hereunder.

          "SERIES F STOCK" means the Series F Cumulative Convertible Preferred
Stock of the Issuer.

          "SERIES H STOCK" means the Series H Cumulative Convertible Preferred
Stock of the Issuer.

          SECTION 1.2    INTERNAL REFERENCES.  Unless the context indicates
otherwise, references to Articles, Sections and paragraphs shall refer to the
corresponding articles, sections and paragraphs in this Agreement, and
references to the parties shall mean the parties to this Agreement.

                                   ARTICLE 2
                              REGISTRATION RIGHTS

          SECTION 2.1    PIGGYBACK REGISTRATIONS.

          (a) Right to Piggyback. Each time the Issuer proposes to register any
of its equity securities under the Securities Act (other than registration
statements relating to employee benefit plans or with respect to corporate
reorganizations or other transactions under Rule 145 of the Securities Act) for
sale to the public, whether for the account of the Issuer or the account of any
securityholder, the Issuer shall give prompt written notice to each Holder of
Registrable Securities, which notice shall be given not less than 20 days prior
to the proposed initial filing date of the Issuer's registration statement and
shall offer each such Holder the opportunity to include in such registration all
or part of the Registrable Securities held by such Holder. Each Holder who
desires to include Registrable Securities in such registration shall so advise
the Issuer in writing (stating the number of Registrable Securities desired to
be registered or sold) within 15 days after the date of such notice from the
Issuer. Any Holder shall have the right to withdraw such Holder's request for
inclusion of such Holder's Registrable Securities in any offering pursuant to
this Section 2.1(a) by giving written notice to the Issuer of such withdrawal.
The Issuer may at any time withdraw or cease proceeding with any such
registration if it shall at the same time withdraw or cease proceeding with the
registration of all other equity securities originally proposed to be
registered.

          (b) Priority on Piggyback Registrations. If the registration statement
under which the Issuer gives notice under this Section 2.1 is for an
underwritten offering, the Issuer shall so advise the Holders of Registrable
Securities. In such event, the right of any such Holder to be included in a
registration pursuant to this Section 2.1 shall be conditioned upon such
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Holder's participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting to the extent provided herein. All
Holders proposing to distribute their Registrable Securities through such
underwriting shall enter into an underwriting agreement in customary form with
the underwriter or underwriters. Notwithstanding any other provision of the
Agreement, if the managing underwriter determines in good faith that marketing
factors require a limitation of the number of securities to be underwritten, the
number of securities that may be included in the underwriting shall be allocated
as follows:

        (i)  with respect to an offering initiated by the Issuer on its own
             behalf, first, to the Issuer, and second to the Holders and any
             other securityholders of the Issuer who have the right to include
             securities in such offering pro rata based on the number of
             securities proposed by such Persons to be included in the offering;
             and

        (ii) with respect to an offering pursuant to demand registration rights
             of securityholders of the Issuer other than the Holders, first to
             the securityholders pursuant to their demand registration rights,
             second to the Issuer, and third, to the Holders and any other
             securityholders of the Issuer who have the right to include
             securities in such offering pro rata based on the number of
             securities proposed by the Holders and such other securityholders
             to be included in such offering.

If as a result of the provisions of this Section 2.1(b) any Holder shall not be
entitled to include all Registrable Securities in an offering that such Holder
has requested to be so included, such Holder may withdraw such Holder's request
to include Registrable Securities in such offering prior to completion of the
offering.

        SECTION 2.2    CERTAIN DELAY RIGHTS.  The Issuer may defer the filing or
effectiveness (but not the preparation) of a registration statement required by
Section 2.1 for a period not to exceed 90 days (or, if longer, 90 days after the
effective date of the registration statement contemplated by clause (ii) or
(iii) below) if (i) at the time the Issuer receives the request contemplated by
Section 2.1, the Issuer or any of its subsidiaries are engaged in confidential
negotiations or other confidential business activities, disclosure of which
would be required in such registration statement (but would not be required if
such registration statement were not filed), and the Board determines in good
faith that such disclosure would be materially detrimental to the Issuer and its
securityholders or would have a material adverse effect on any such confidential
negotiations or other confidential business activities, (ii) within ten (10)
business days following its receipt of a Demand Request or Form S-3 Request, the
Issuer decides to effect a public offering of the Issuer's securities of the
same class as Registrable Securities for the Issuer's account, or (iii) prior to
the receipt of any Demand Request or Form S-3 Request, another Person has
exercised demand registration rights and the Issuer has begun preparations or
planning for the offering.  A deferral of the filing or effectiveness of a
registration statement pursuant to this Section 2.2 shall be lifted, and the
requested registration statement shall be filed forthwith, if, in the case of a
deferral pursuant to clause (i) of the preceding sentence, the negotiations or
other activities are disclosed or terminated, or, in the case of a deferral
pursuant to clause (ii) or (iii) of the preceding sentence, the proposed
offering for the Issuer's or another securityholder's account is abandoned.  In
order to defer the filing or effectiveness of a
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registration statement pursuant to this Section 2.2, the Issuer shall promptly
(but in any event within three (3) business days), upon determining to seek such
deferral, deliver to each Holder a certificate signed by an executive officer of
the Issuer stating that the Issuer is deferring such filing pursuant to this
Section 2.2 and a general statement of the reason for such deferral, and an
approximation of the anticipated delay. Within 20 days after receiving such
certificate, the holders of a majority of the Registrable Securities held by the
Requesting Holders or the Holder who delivered the Form S-3 Request and for
which registration was previously requested may withdraw such Demand Request or
Form S-3 Request, as applicable, by giving notice to the Issuer. If withdrawn,
the Demand Request or Form S-3 Request, as applicable, shall be deemed not to
have been made for all purposes of this Agreement other than this Section 2.2.
The Issuer may defer the filing of a particular registration statement pursuant
to this Section 2.2 only once during any 12-month period.

        SECTION 2.3    EXPENSES.  Except as provided herein, the Issuer shall be
responsible for all Registration Expenses with respect to each registration
hereunder, whether or not any registration statement becomes effective.
Notwithstanding the foregoing; (i) each Holder shall be responsible for all
underwriting discounts, selling commissions and transfer taxes, if any, in
connection with the sale of securities by such Holder, and (ii) the Issuer shall
be responsible for all out-of-pocket costs and expenses of the Issuer and its
officers and employees incurred in connection with providing the assistance
and/or attending analyst or investor presentations or any "road show" undertaken
in connection with the registration and/or marketing of any Registrable
Securities as contemplated in Section 2.4(g).

        SECTION 2.4    REGISTRATION AND QUALIFICATION.  If and whenever the
Issuer is required to effect the registration of any Registrable Securities
under the Securities Act as provided in Section 2.1, the Issuer shall as
promptly as practicable (but subject to the provisions of Section 2.1):

        (a) prepare, file and cause to become effective a registration statement
under the Securities Act relating to the Registrable Securities to be offered in
accordance with the intended method of disposition thereof;

        (b) prepare and file with the Commission such amendments and supplements
to such registration statement and the prospectus used in connection therewith
as may be necessary to keep such registration statement effective and to comply
with the provisions of the Securities Act with respect to the disposition of all
Registrable Securities until the earlier of (i) such time as all Registrable
Securities proposed to be sold therein have been disposed of in accordance with
the intended methods of disposition set forth in such registration statement and
(ii) the expiration of 180 days after such registration statement becomes
effective, provided, that such 180-day period shall be extended for such number
of days that equals the number of days elapsing from (x) the date the written
notice contemplated by Section 2.4(e) below is given by the Issuer to (y) the
date on which the Issuer delivers to the Holders of Registrable Securities the
supplement or amendment contemplated by Section 2.4(e) below;

        (c) furnish to the Holders of Registrable Securities and to any
underwriter of such Registrable Securities such number of conformed copies of
such registration statement and of each such amendment and supplement thereto
(in each case including all exhibits), such
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number of copies of the prospectus included in such registration statement
(including each preliminary prospectus) in conformity with the requirements of
the Securities Act and such documents incorporated by reference in such
registration statement or prospectus as the Holders of Registrable Securities or
such underwriter may reasonably request (it being understood that, subject to
Section 2.8 and the requirements of the Securities Act and applicable state
securities law, the Issuer consents to the use of the prospectus and any
amendment or supplement thereto by each Selling Holder and the underwriters in
connection with the offering and sale of the Registrable Securities covered by
the registration statement of which such prospectus, amendment to supplement is
a part);

        (d) use its reasonable best efforts to obtain an opinion of counsel for
the Issuer and a "cold comfort" letter signed by the independent public
accountants who have audited the financial statements of the Issuer included in
or incorporated by reference into the applicable registration statement, in each
such case covering substantially such matters with respect to such registration
statement (and the prospectus included therein) and the related offering as are
customarily covered in opinions of issuer's counsel with respect thereto and in
accountants' letters delivered to underwriters in underwritten public offerings
of securities and such other matters as such underwriters may reasonably request
and furnish to each underwriter a copy of such opinion and such letter;

        (e) promptly notify the Selling Holders and each underwriter in writing
(i) when a prospectus or any prospectus supplement or post-effective amendment
has been filed and, with respect to a registration statement or any post-
effective amendment, when the same has become effective, (ii) of the issuance by
any state securities or other regulatory authority of any order suspending the
qualification or exemption from qualification of any of the Registrable
Securities under state securities or "blue sky" laws or the initiation of any
proceedings for that purpose, (iii) at any time when a prospectus relating to a
registration pursuant to Section 2.1 is required to be delivered under the
Securities Act, of the happening of any event that the Issuer becomes aware of,
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state any material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances under which they were made,
not misleading, and (iv) of any request by the Commission, or any other
regulatory body or other body having jurisdiction, for any amendment or
supplement to any registration statement or other document relating to such
offering, and in either such case, at the request of the Selling Holders,
promptly prepare and furnish to the Selling Holders a reasonable number of
copies of a supplement to or an amendment of such prospectus as may be necessary
so that, as thereafter delivered to the purchasers of such Registrable
Securities, such prospectus shall not include an untrue statement of a material
fact or omit to state a material fact required to be stated therein or necessary
to make the statements therein, in light of the circumstances under which they
are made, not misleading;

        (f) use its reasonable best efforts to list all such Registrable
Securities covered by such registration on each securities exchange or automated
interdealer quotation system on which the Common Stock is then listed;

        (g) use its reasonable best efforts to assist the Holders in the
marketing of Common Stock in connection with underwritten offerings hereunder
(including, to the extent
<PAGE>

reasonably consistent with work commitments, using reasonable efforts to have
officers of the Issuer attend "road shows" and analyst or investor presentations
scheduled in connection with such registration), with all out-of-pocket costs
and expenses incurred by the Issuer or such officers in connection with such
attendance or assistance to be paid by the Issuer as provided in Section 2.3;

        (h) use its reasonable best efforts to register or qualify such
Registrable Securities under such other securities or blue sky laws of such
jurisdictions as the managing underwriter reasonably requests; use its
reasonable best efforts to keep each such registration or qualification (or
exemption therefrom) effective during the period in which such registration
statement is required to be kept effective; and do any and all other acts and
things which may be reasonably necessary or advisable to enable such Selling
Holder to consummate the disposition of the Registrable Securities owned by such
Selling Holder in such jurisdictions (provided, however, that the Issuer will
not be required to (A) qualify generally to do business in any jurisdiction
where it would not otherwise be required to qualify but for this subparagraph or
(B) consent to general service of process in any such jurisdiction);

        (i) make generally available to the Holders an earning statement
satisfying the provisions of Section 11(a) of the Securities Act no later than
30 days after the end of the 12-month period beginning with the first day of the
Issuer's first fiscal quarter commencing after the effective date of a
registration statement, which earnings statement shall cover said 12-month
period, and which requirement will be deemed to be satisfied if the Issuer
timely files complete and accurate information on Forms 10-Q, 10-K and 8-K under
the Exchange Act, and otherwise complies with Rule 158 under the Securities Act;

        (j) if requested by the managing underwriter or any Selling Holder,
promptly incorporate in a prospectus supplement or post-effective amendment such
information as the managing underwriter or any Selling Holder reasonably
requests to be included therein, including, without limitation, with respect to
the Registrable Securities being sold by such Selling Holder, the purchase price
being paid therefor by the underwriters and with respect to any other terms of
the underwritten offering of the Registrable Securities to be sold in such
offering, and promptly make all required filings of such prospectus supplement
or post-effective amendment;

        (k) as promptly as practicable after filing with the Commission of any
document which is incorporated by reference into a registration statement (in
the form in which it was incorporated), deliver a copy of each such document to
each Selling Holder;

        (l) provide a CUSIP number for the Registrable Securities included in
any registration statement not later than the effective date of such
registration statement;

        (m) cooperate with each Selling Holder and each underwriter
participating in the disposition of such Registrable Securities and their
respective counsel in connection with any filings required to be made with the
National Association of Securities Dealers, Inc.;

        (n) prepare and file with the Commission promptly any amendments or
supplements to such registration statement or prospectus which, in the opinion
of counsel for the
<PAGE>

Issuer or the managing underwriter, is required in connection with the
distribution of the Registrable Securities; and

        (o) advise each Selling Holder of such Registrable Securities, promptly
after it shall receive notice or obtain knowledge thereof, of the issuance of
any stop order by the Commission suspending the effectiveness of such
registration statement or the initiation or threatening of any proceeding for
such purpose and promptly use its best efforts to prevent the issuance of any
stop order or to obtain its withdrawal at the earliest possible moment if such
stop order should be issued.

        SECTION 2.5    UNDERWRITING; DUE DILIGENCE.

        (a) If requested by the underwriters for any underwritten offering of
Registrable Securities pursuant to a registration requested under this Article
2, the Issuer shall enter into an underwriting agreement with such underwriters
for such offering, which agreement will contain such representations and
warranties by the Issuer and such other terms and provisions as are customarily
contained in underwriting agreements with respect to secondary distributions,
including, without limitation, indemnification and contribution provisions
substantially to the effect and to the extent provided in Section 2.6, and
agreements as to the provision of opinions of counsel and accountants' letters
to the effect and to the extent provided in Section 2.4(d). Such underwriting
agreement shall also contain such representations and warranties by such Selling
Holders and such other terms and provisions as are customarily contained in
underwriting agreements with respect to secondary distributions, including,
without limitation, indemnification and contribution provisions substantially to
the effect and to the extent provided in Section 2.6.

        (b) In connection with the preparation and filing of each registration
statement registering Registrable Securities under the Securities Act pursuant
to this Article 2, the Issuer shall give the Selling Holders and the
underwriters, if any, and their respective counsel and accountants, such
reasonable and customary access to its books, records and properties and such
opportunities to discuss the business and affairs of the Issuer with its
officers and the independent public accounts who have certified the financial
statements of the Issuer as shall be necessary, in the opinion of such Holders
and such underwriters or their respective counsel, to conduct a reasonable
investigation within the meaning of the Securities Act; provided that (i) each
Holder and the underwriters and their respective counsel and accountants shall
have entered into a confidentiality agreement reasonably acceptable to the
Issuer and (ii) each Holder and the underwriters and their respective counsel
and accountants shall use their reasonable best efforts to minimize the
disruption to the Issuer's business and coordinate any such investigation of the
books, records and properties of the Issuer and any such discussions with the
Issuer's officers and accountants so that all such investigations occur at the
same time and all such discussions occur at the same time.

        SECTION 2.6    INDEMNIFICATION AND CONTRIBUTION.

        (a) The Issuer agrees to indemnify and hold harmless, to the fullest
extent permitted by law, each Selling Holder and each of its employees,
advisors, agents, representatives, partners, officers and directors, and each
Person, if any, who controls such
<PAGE>

Selling Holder within the meaning of either Section 15 of the Securities Act or
Section 20 of the Exchange Act from and against any and all losses, claims,
damages, liabilities or expenses (including, without limitation, any legal or
other expenses reasonably incurred in connection with defending or investigating
any such action or claim) ("LOSSES") insofar as such Losses are caused by any
untrue statement or alleged untrue statement of a material fact contained in any
registration statement or any amendment thereof, any preliminary prospectus or
prospectus (as amended or supplemented if the Issuer shall have furnished any
amendments or supplements thereto) relating to the Registrable Securities, or
caused by any omission or alleged omission to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, or caused by any violation or alleged violation by the Issuer of the
Securities Act, the Exchange Act, any state securities laws or any rule or
regulation promulgated under the Securities Act, the Exchange Act or any state
securities laws, except insofar as such Losses are caused by any such untrue
statement or omission or alleged untrue statement or omission made in reliance
upon information furnished to the Issuer in writing by such Selling Holder (or
any representative thereof) expressly for use therein. The Issuer also agrees to
indemnify any underwriter of the Registrable Securities so offered and each
Person, if any, who controls such underwriter on substantially the same basis as
that of the indemnification by the Issuer of the Selling Holders provided in
this Section 2.6(a). The reimbursement required by this Section 2.6(a) will be
made by periodic payments during the course of the investigation or defense, as
and when bills are received or expenses incurred.

        (b) Each Selling Holder agrees to indemnify and hold harmless the
Issuer, its employees, advisors, agents, representatives, directors, the
officers who sign the registration statement and each Person, if any who
controls the Issuer within the meaning of either Section 15 of the Securities
Act or Section 20 of the Exchange Act, from and against any and all Losses,
insofar as such Losses are caused by any untrue statement or alleged untrue
statement of a material fact contained in any registration statement or any
amendment thereof, any preliminary prospectus or prospectus (as amended or
supplemented if the Issuer shall have furnished any amendments or supplements
thereto) relating to the Registrable Securities, or caused by any omission or
alleged omission to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading, but only with
reference to information furnished in writing by such Selling Holder (or any
representative thereof) expressly for use in a registration statement, any
preliminary prospectus, prospectus or any amendments or supplements thereto;
provided that the obligation to indemnify will be several, not joint and
several, among such Selling Holders, and the liability of each Selling Holder
will be in proportion to, and provided further that such liability will be
limited to, the net amount received by such seller from the sale of Registrable
Securities pursuant to such registration statement; provided, however, that such
Selling Holder shall not be liable in any such case to the extent that prior to
the filing of any such registration statement or prospectus or amendment thereof
or supplement thereto, such Selling Holder has furnished in writing to the
Issuer information expressly for use in such registration statement or
prospectus or any amendment or supplement thereto which corrected or made not
misleading information previously furnished to the Issuer. Each Selling Holder
also agrees to indemnify any underwriter of the Registrable Securities so
offered and each Person, if any, who controls such underwriter on substantially
the same basis as that of the indemnification by such Selling Holder of the
Issuer provided in this Section 2.6(b).
<PAGE>

        (c) Each party indemnified under paragraph (a) or (b) above shall,
promptly after receipt of notice of a claim or action against such indemnified
party in respect of which indemnity may be sought hereunder, notify the
indemnifying party in writing of the claim or action; provided that the failure
to notify the indemnifying party shall not relieve it from any liability that it
may have to an indemnified party on account of the indemnity agreement contained
in paragraph (a) or (b) above except to the extent that the indemnifying party
was actually prejudiced by such failure, and in no event shall such failure
relieve the indemnifying party from any other liability that it may have to such
indemnified party. If any such claim or action shall be brought against an
indemnified party, and it shall have notified the indemnifying party thereof,
unless based on the written advice of counsel to such indemnified party a
conflict of interest between such indemnified party and indemnifying parties may
exist in respect of such claim, the indemnifying party shall be entitled to
participate therein, and, to the extent that it wishes, jointly with any other
similarly notified indemnifying party, to assume the defense thereof. After
notice from the indemnifying party to the indemnified party of its election to
assume the defense of such claim or action, the indemnifying party shall not be
liable to the indemnified party under this Section 2.6 for any legal or other
expenses subsequently incurred by the indemnified party in connection with the
defense thereof. Any indemnifying party against whom indemnity may be sought
under this Section 2.6 shall not be liable to indemnify an indemnified party if
such indemnified party settles such claim or action without the consent of the
indemnifying party. The indemnifying party may not agree to any settlement of
any such claim or action, other than solely for monetary damages for which the
indemnifying party shall be responsible hereunder, the result of which any
remedy or relief shall be applied to or against the indemnified party, without
the prior written consent of the indemnified party, which consent shall not be
unreasonably withheld and unless such settlement contains a full and
unconditional release of the indemnified party. In any action hereunder as to
which the indemnifying party has assumed the defense thereof, the indemnified
party shall continue to be entitled to participate in the defense thereof, with
counsel of its own choice, but the indemnifying party shall not be obligated
hereunder to reimburse the indemnified party for the costs thereof.

        (d) If the indemnification provided for in this Section 2.6 shall for
any reason be unavailable (other than in accordance with its terms) to an
indemnified party in respect of any Loss referred to herein, then each
indemnifying party shall, in lieu of indemnifying such indemnified party,
contribute to the amount paid or payable by such indemnified party as a result
of such Loss in such proportion as is appropriate to reflect the relative fault
of the indemnifying party or parties on the one hand and of the indemnified
party or parties on the other hand in connection with the statements or
omissions that resulted in such Losses, as well as any other relevant equitable
considerations. The relative fault of the Issuer on the one hand and the Selling
Holders on the other hand shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by the Issuer or a Selling Holder and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission. The amount paid or payable by an indemnified party as a
result of the Loss, or action in respect thereof, referred to above in this
paragraph (d) shall be deemed to include, for purposes of this paragraph (d),
any legal or other expenses reasonably incurred by such indemnified party in
connection with investigating or defending any such action or claim. The Issuer
and the Selling Holders agree that it would not be just and equitable if
contribution pursuant to this Section 2.6 were determined by pro rata allocation
or by any other method of
<PAGE>

allocation which does not take account of the equitable considerations referred
to in this paragraph. Notwithstanding any other provision of this Section 2.6,
no Selling Holder shall be required to contribute any amount in excess of the
amount by which the total price at which the Registrable Securities of such
Selling Holder were offered to the public exceeds the amount of any damages
which such Selling Holder has otherwise been required to pay by reason of such
untrue or alleged untrue statement or omission or alleged omission. No Person
guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of
the Securities Act) shall be entitled to contribution from any Person who was
not guilty of such fraudulent misrepresentation. The Holders' obligations in
this Section 2.6(d) to contribute shall be several in proportion to the amount
of Registrable Securities registered by them and not joint.

        (e) The obligations of the parties under this Section 2.6 shall be in
addition to any liability which any party may otherwise have to any other party.

        SECTION 2.7 AVAILABLE INFORMATION. The Issuer agrees to use its
reasonable best efforts to:

        (a) Make and keep public information available, as those terms are
understood and defined in Rule 144;

        (b) File with the Commission, in a timely manner, all reports and other
documents required of the Issuer under the Exchange Act; and

        (c) furnish to a Holder forthwith upon request: a written statement by
the Issuer as to its compliance with the reporting requirements of Rule 144 and
of the Exchange Act; a copy of the most recent annual or quarterly report of the
Issuer; and such other reports and documents as a Holder may reasonably request
in availing itself of any rule or regulation of the Commission allowing it to
sell any of the Issuer's securities without registration.

        SECTION 2.8 SUSPENSION OF DISPOSITIONS. Each Holder agrees by
acquisition of any Registrable Securities that, upon receipt of any notice (a
"SUSPENSION NOTICE") from the Issuer of the happening of any event of the kind
described in Section 2.4(e)(iii), such Holder will forthwith discontinue
disposition of Registrable Securities until such Holder's receipt of the copies
of the supplemented or amended prospectus, or until it is advised in writing
(the "ADVICE") by the Issuer that the use of the prospectus may be resumed, and
has received copies of any additional or supplemental filings which are
incorporated by reference in the prospectus, and, if so directed by the Issuer,
such Holder will deliver to the Issuer all copies, other than permanent file
copies then in such Holder's possession, of the prospectus covering such
Registrable Securities current at the time of receipt of such notice. In the
event the Issuer shall give any such notice, the time period regarding the
effectiveness of registration statements set forth in Section 2.4(b) hereof
shall be extended by the number of days during the period from and including the
date of the giving of the Suspension Notice to and including the date when each
Selling Holder of Registrable Securities covered by such registration statement
shall have received the copies of the supplemented or amended prospectus or the
Advice. The Issuer shall use its best efforts and take such actions as are
reasonably necessary to render the Advice as promptly as practicable.
<PAGE>

                                   ARTICLE 3
                                 MISCELLANEOUS

        SECTION 3.1 ENTIRE AGREEMENT. This Agreement constitutes the entire
agreement between the parties with respect to the subject matter hereof and
supersedes all other prior agreements and understandings, both written and oral,
between the parties with respect to the subject matter hereof. The parties agree
that this Agreement shall not modify or otherwise affect any of the registration
rights of the Holders and the obligations of the Issuer relating thereto under
(i) that certain Stock Purchase Agreement dated December 15, 1999 (as amended),
by and among the Issuer, the Holders and other parties relating to the purchase
and sale of the Series F Stock and (ii) that certain Stock Purchase Agreement
dated July 30, 1998 (as amended), by and among the Issuer, the Holders and other
parties relating to the purchase and sale of the Series H Stock (which was
acquired by exchange of Series G Cumulative Preferred Stock of the Issuer that
was acquired by exchange of Series E Cumulative Preferred Stock of the Issuer).

        SECTION 3.2 NO CONFLICTING RIGHTS. The Issuer represents and warrants
that no other Person has registration rights that conflict with the rights
granted to the Holders hereunder.

        SECTION 3.3 ASSIGNMENT. Except as otherwise provided herein, no party
may assign any of its rights or obligations hereunder, by operation of law or
otherwise, without the prior written consent of the other parties. A Holder may
assign its rights and interests hereunder to any Affiliate of the Holder.
Subject to the provisions of this Section 3.3, each transferee shall be a
"Holder" for all purposes under this Agreement upon execution and delivery of
its written agreement to be bound by the terms hereof.

        SECTION 3.4 AMENDMENTS, WAIVERS, ETC. This Agreement may not be amended,
changed, supplemented, waived or otherwise modified or terminated, except upon
the execution and delivery of a written agreement executed by the Issuer and
Holders representing a majority of the Registrable Securities then held by all
Holders.

        SECTION 3.5 NOTICES. All notices under this Agreement shall be in
writing and shall be deemed to have been received (a) when personally delivered
or sent by telecopy, (b) one day following delivery by overnight delivery
courier, with all delivery charges pre-paid, or (c) on the third business day
following the date on which it was sent by United States mail, postage prepaid,
to a party at the address or fax number, as the case may be, of such party as
set forth on the signature page of this Agreement or such other address as a
party may specify in writing.

        SECTION 3.6 SEVERABILITY. Whenever possible, each provision or portion
of any provision of this Agreement will be interpreted in such manner as to be
effective and valid under applicable law but if any provision or portion of any
provision of this Agreement is held to be invalid, illegal or unenforceable in
any respect under any applicable law or rule in any jurisdiction, such
invalidity, illegality or unenforceability will not affect any other provision
or portion of any provision in such jurisdiction, and this Agreement will be
reformed, construed and enforced in such jurisdiction as if such invalid,
illegal or unenforceable provision or portion of any provision had never been
contained herein.
<PAGE>

        SECTION 3.7 NO WAIVER. The failure of any party hereto to exercise any
right, power or remedy provided under this Agreement or otherwise available in
respect hereof at law or in equity, or to insist upon compliance by any other
party hereto with its obligations hereunder, and any custom or practice of the
parties at variance with the terms hereof, shall not constitute a waiver by such
party of its right to exercise any such or other right, power or remedy or to
demand such compliance.

        SECTION 3.8 NO THIRD PARTY BENEFICIARIES. This Agreement is not intended
to be for the benefit of, and shall not be enforceable by, any Person who or
which is not a party hereto; provided, that, this Agreement is also intended to
be for the benefit of and is enforceable by each Holder.

        SECTION 3.9 GOVERNING LAW. This Agreement will be governed by and
construed in accordance with the laws of the State of Texas other than the
conflict of laws rules thereof.

        SECTION 3.10 DESCRIPTIVE HEADINGS. The descriptive headings used herein
are inserted for convenience of reference only and are not intended to be part
of or to affect the meaning or interpretation of this Agreement.

        SECTION 3.11 COUNTERPARTS. This Agreement may be executed in
counterpart, each of which shall be deemed to be an original, but all of which,
taken together, shall constitute one and the same agreement.

                            [Signature page follows]
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed as of the date first above written.


                              PLAINS RESOURCES INC.


                              By: /s/ James C. Flores
                                 -----------------------------------
                              Name:  James C. Flores
                                   ---------------------------------
                              Title: Chairman and Chief Executive
                                     Officer
                                    --------------------------------

                              Address:  500 Dallas Street
                                        Houston, Texas 77002

                              Facsimile No.:  (713) 654-1523



                              ENCAP ENERGY CAPITAL FUND III, L.P.

                              By: EnCap Investments L.L.C.,
                                  its general partner


                              By:  /s/ Gary R. Peterson
                                 -----------------------------------
                              Name: Gary R. Peterson
                                   ---------------------------------
                              Title: Managing Director
                                    --------------------------------

                              Address:  c/o EnCap Investments L.L.C.
                                        1100 Louisiana, Suite 3150
                                        Houston, Texas  77002

                              Facsimile No.:  (713) 659-6130



                                      S-1
<PAGE>

                              ENCAP ENERGY CAPITAL FUND III-B, L.P.

                              By: EnCap Investments L.L.C.,
                                  its general partner


                              By: /s/ Gary R. Peterson
                                 -----------------------------------
                              Name: Gary R. Peterson
                                   ---------------------------------
                              Title: Managing Director
                                    --------------------------------

                              Address:  c/o EnCap Investments L.L.C.
                                        1100 Louisiana, Suite 3150
                                        Houston, Texas  77002

                              Facsimile No.:  (713) 659-6130



                              BOCP ENERGY PARTNERS, L.P.

                              By: EnCap Investments L.L.C.,
                                  its Manager


                              By: /s/ Gary R. Peterson
                                 -----------------------------------
                              Name: Gary R. Peterson
                                   ---------------------------------
                              Title: Managing Director
                                    --------------------------------

                              Address:  c/o EnCap Investments L.L.C.
                                        1100 Louisiana, Suite 3150
                                        Houston, Texas  77002

                              Facsimile No.:  (713) 659-6130


                                      S-2

<PAGE>

                              ENERGY CAPITAL INVESTMENT
                              COMPANY PLC


                              By: /s/ Gary R. Peterson
                                 -----------------------------------
                              Name: Gary R. Peterson
                                   ---------------------------------
                              Title: Director
                                    --------------------------------

                              Address:  c/o EnCap Investments L.L.C.
                                        1100 Louisiana, Suite 3150
                                        Houston, Texas  77002

                              Facsimile No.:  (713) 659-6130





                                      S-3