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EXHIBIT 10.3

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AMENDED AND RESTATED

OMNIBUS AGREEMENT

among

PLAINS RESOURCES INC.

PLAINS ALL AMERICAN PIPELINE, L.P.

PLAINS MARKETING, L.P.

PLAINS PIPELINE, L.P.

and

PLAINS ALL AMERICAN GP LLC

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TABLE OF CONTENTS

ARTICLE I Definitions   1   1.1 Definitions   1
ARTICLE II Business Opportunities
 
2   2.1 Restricted Businesses   2   2.2 Permitted Exceptions   2   2.3
Procedures   3   2.4 Termination   4   2.5 Scope of Restricted Business
Prohibition   4   2.6 Enforcement   4
ARTICLE III Miscellaneous
 
5   3.1 Choice of Law; Submission to Jurisdiction   5   3.2 Notice   5   3.3
Entire Agreement; Supersedure   5   3.4 Effect of Waiver or Consent   5   3.5
Amendment or Modification   5   3.6 Assignment   5   3.7 Counterparts   5   3.8
Severability   5   3.9 Gender, Parts, Articles and Sections   6   3.10 Further
Assurances   6   3.11 Withholding or Granting of Consent   6   3.12 U.S.
Currency   6   3.13 Laws and Regulations   6   3.14 Negotiation of Rights of
Limited Partners, Assignees, and Third Parties   6

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AMENDED AND RESTATED OMNIBUS AGREEMENT

        THIS AMENDED AND RESTATED OMNIBUS AGREEMENT, dated as of July 23, 2004,
among Plains Resources Inc., a Delaware corporation ("Plains Resources"), Plains
All American Pipeline, L.P., a Delaware limited partnership (the "MLP"), Plains
All American GP LLC, a Delaware corporation ("GP LLC"), Plains Marketing
GP Inc., a Delaware corporation ("GP Inc."), Plains Marketing, L.P., a Texas
limited partnership ("Operating OLP"), and Plains Pipeline, L.P., a Texas
limited partnership ("Plains OLP" and, together with Operating OLP, the "OLPs")
amends and restates that certain Omnibus Agreement dated as of November 23, 1998
among Plains Resources, Plains All American Inc., a Delaware corporation, the
MLP and the predecessors to the OLPs.

R E C I T A L S:

        Plains Resources, the MLP, the OLPs and GP LLC, in its capacity as the
general partner of the general partner of the MLP and GP Inc., in its capacity
as the general partner of the OLPs, desire by their execution of this Agreement
to evidence their understanding, as more fully set forth in Article II of this
Agreement, with respect to (a) those business opportunities that Plains
Resources will not avail itself of during the Applicable Period unless each of
the MLP and the OLPs has declined to engage in such business opportunity for its
own account and (b) the procedures whereby such business opportunities are to be
offered to the MLP and the OLPs and accepted or declined.

        In consideration of the premises and the covenants, conditions, and
agreements contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
hereby agree as follows:

ARTICLE I
Definitions

        1.1   Definitions.

        (a)   Capitalized terms used herein but not defined shall have the
meanings given them in the MLP Agreement.

        (b)   As used in this Agreement, the following terms shall have the
respective meanings set forth below:

        "Affiliate" shall mean, with respect to any Person, any other Person
that directly or indirectly through one or more intermediaries controls, is
controlled by or is under common control with, the Person in question. As used
herein, the term "control" means the possession, direct or indirect, of the
power to direct or cause the direction of the management and policies of a
Person, whether through ownership of voting securities, by contract or
otherwise. For clarity, Plains Exploration & Production Company and Plains
Resources are not Affiliates of each other for purposes of this Agreement.

        "Agreement" shall mean this Amended and Restated Omnibus Agreement, as
it may be amended, modified, or supplemented from time to time.

        "Applicable Period" shall mean the period commencing on November 23,
1998 and terminating on the date on which no Plains Entity owns, directly or
indirectly, an interest in the general partner of the MLP.

        "Conflicts Committee" shall have the meaning attributed to such term in
the MLP Agreement.

        "General Partner" shall mean GP LLC and its successors as general
partner of the general partner the MLP, unless the context otherwise requires.

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        "LLC Agreement" shall mean the Amended and Restated Limited Liability
Company Agreement dated as of June 8, 2001, as amended September 16, 2003 and as
may be amended from time to time.

        "Marketing Agreement" shall mean that Amended and Restated Crude Oil
Marketing Agreement dated as of the date hereof among Plains Resources, Calumet
Florida LLC and Operating OLP.

        "MLP Agreement" shall mean the Third Amended and Restated Agreement of
Limited Partnership of the MLP, dated as of June 27, 2001, as amended on
April 15, 2004, and as such agreement may be amended from time to time, to which
reference is hereby made for all purposes of this Agreement.

        "Non-Affiliate Purchaser" shall have the meaning attributed to such term
in Section 2.3.

        "Offer" shall have the meaning attributed to such term in Section 2.3.

        "Partnership Entities" shall mean the General Partner, the MLP, the OLPs
and any Affiliate controlled by the General Partner, the MLP or the OLPs.

        "Partnership Group" shall mean the MLP, the OLPs and any subsidiary of
any such entities.

        "Person" shall mean an individual, corporation, partnership, joint
venture, trust, limited liability company, unincorporated organization or any
other entity.

        "Plains Entities" shall mean Plains Resources and any of its Affiliates,
other than the Partnership Entities.

        "Restricted Business" shall have the meaning attributed to such term in
Section 2.1.

        "Second Offer" shall have the meaning attributed to such term in
Section 2.3.

ARTICLE II
Business Opportunities

        2.1   Restricted Businesses. During the Applicable Period, each of the
Plains Entities shall be prohibited from engaging in or acquiring any business
engaged in the following activities (a "Restricted Business"): (a) crude oil
storage, terminalling and gathering activities in any state in the United States
(except for Hawaii), the Outer Continental Shelf of the United States or any
province or territory in Canada, for any Person other than a Plains Entity or
Partnership Entity, (b) crude oil marketing activities, and (c) transportation
of crude oil by pipeline in any state in the United States (except for Hawaii),
the Outer Continental Shelf of the United States or any province or territory in
Canada, for any Person other than a Plains Entity. A Restricted Business shall
not include any activities required to be performed by a Plains Entity as the
operator pursuant to any operating agreement entered into by such Plains Entity
with respect to oil and gas properties owned jointly with other Persons.

        2.2   Permitted Exceptions. Notwithstanding any provision of Section 2.1
to the contrary, a Plains Entity may engage in a Restricted Business under the
following circumstances:

        (a)   The Restricted Business was engaged in by the Plains Entity on
November 23, 1998.

        (b)   The Restricted Business is conducted pursuant to and in accordance
with the terms of the Marketing Agreement or any other arrangement entered into
with the MLP or either of the OLPs with the concurrence of the Conflicts
Committee.

        (c)   The value of the assets acquired in a transaction that comprise a
Restricted Business does not exceed $10 million, as determined by the Board of
Directors of Plains Resources.

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        (d)   (i) The value of the assets acquired in a transaction that
comprise a Restricted Business exceed $10 million, as determined by the Board of
Directors of Plains Resources and (ii) the General Partner (with the approval of
the Conflicts Committee) has elected not to cause a member of the Partnership
Group to pursue such opportunity in accordance with the procedures set forth in
Section 2.3.

        2.3   Procedures. In the event that a Plains Entity acquires a
Restricted Business comprised of assets valued in excess of $10 million, as
determined by the Board of Directors of Plains Resources, then not later than
30 days after the consummation of the acquisition by such Plains Entity of the
Restricted Business, such Plains Entity shall notify the General Partner of such
purchase and offer the Partnership the opportunity to purchase such Restricted
Business. As soon as practicable, but in any event, within 30 days after receipt
of such notification, the General Partner shall notify the Plains Entity that
either (i) the General Partner has elected, with the approval of the Conflicts
Committee, not to cause a member of the Partnership Group to purchase such
Restricted Business, in which event the Plains Entity shall be free to continue
to engage in such Restricted Business, or (ii) the General Partner has elected
to cause a member of the Partnership Group to purchase such Restricted Business,
in which event the following procedures shall be followed:

        (a)   The Plains Entity shall submit a good faith offer to the General
Partner to sell the Restricted Business (the "Offer") to any member of the
Partnership Group on the terms and for the consideration stated in the Offer.

        (b)   The Plains Entity and the General Partner shall negotiate in good
faith, for 60 days after receipt of such Offer by the General Partner, the terms
on which the Restricted Business will be sold to a member of the Partnership
Group. The Plains Entity shall provide all information concerning the business,
operations and finances of such Restricted Business as may be reasonably
requested by the General Partner.

        (i)    If the Plains Entity and the General Partner agree on such terms
within 60 days after receipt by the General Partner of the Offer, a member of
the Partnership Group shall purchase the Restricted Business on such terms as
soon as commercially practicable after such agreement has been reached.

        (ii)   If the Plains Entity and the General Partner are unable to agree
on the terms of a sale during such 60-day period, the Plains Entity shall
attempt to sell the Restricted Business to a Person that is not an Affiliate of
the Plains Entity (a "Non-Affiliate Purchaser") within nine months of the
termination of such 60-day period. Any such sale to a Non-Affiliate Purchaser
must be for a purchase price, as determined by the Board of Directors of Plains
Resources, not less than 95% of the purchase price last offered by a member of
the Partnership Group.

        (c)   If, after the expiration of such nine-month period, the Plains
Entity has not sold the Restricted Business to a Non-Affiliate Purchaser, it
shall submit another Offer (the "Second Offer") to the General Partner within
seven days after the expiration of such nine-month period. The Plains Entity
shall provide all information concerning the business, operations and finances
of such Restricted Business as may be reasonably requested by the General
Partner.

        (i)    If the General Partner, with the concurrence of the Conflicts
Committee, elects not to cause a member of the Partnership Group to pursue the
Second Offer, the Plains Entity shall be free to continue to engage in such
Restricted Business.

        (ii)   If the General Partner shall elect to cause a member of the
Partnership Group to purchase such Restricted Business, then the General Partner
and the Plains Entity shall negotiate the terms of such purchase for 60 days. If
the Plains Entity and the General Partner agree on such terms within 60 days
after receipt by the General Partner of the Second Offer,

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a member of the Partnership Group shall purchase the Restricted Business on such
terms as soon as commercially practicable after such agreement has been reached.

        (iii)  If during such 60-day period, no agreement has been reached
between the Plains Entity and the General Partner or a member of the
Partnership, the Plains Entity and the General Partner will engage an
independent investment banking firm with a national reputation to determine the
value of the Restricted Business. Such investment banking firm will determine
the value of the Restricted Business within 30 days and furnish the Plains
Entity and the General Partner its opinion of such value. The Plains Entity will
pay the fees and expenses of such investment banking firm. Upon receipt of such
opinion, the General Partner will have the option, subject to the approval of
the Conflicts Committee, to (A) cause a member of the Partnership Group to
purchase the Restricted Business for an amount equal to the value determined by
such investment banking firm or (B) decline to purchase such Restricted
Business, in which event the Plains Entity will be free to continue to engage in
such Restricted Business.

        2.4   Termination. The provisions of this Article II may be terminated
by Plains Resources upon a "Change of Control" of Plains Resources. A Change of
Control of Plains Resources shall be deemed to have occurred upon the occurrence
of one or more of the following events: (i) any sale, lease, exchange or other
transfer (in one transaction or a series of related transactions) of all or
substantially all of the assets of the Plains Entities to any Person and its
Affiliates unless immediately following such sale, lease, exchange or other
transfer such assets are owned, directly or indirectly, by the Plains Entities;
(ii) the consolidation or merger of Plains Resources with or into another Person
pursuant to a transaction in which the outstanding Voting Stock of Plains
Resources is changed into or exchanged for cash, securities or other property,
other than any such transaction where (a) the outstanding Voting Stock of Plains
Resources is changed into or exchanged for Voting Stock of the surviving
corporation or its parent and (b) the holders of the Voting Stock of Plains
Resources immediately prior to such transaction own, directly or indirectly, not
less than a majority of the Voting Stock of the surviving corporation or its
parent immediately after such transaction; and (iii) a "person" or "group"
(within the meaning of Sections 13(d) or 14(d)(2) of the Exchange Act) being or
becoming the "beneficial owner" (as defined in Rules 13d-3 and 13d-5 under the
Exchange Act) of more than 50% of all Voting Stock of Plains Resources, then
outstanding, except in a merger or consolidation which would not constitute a
Change of Control under clause (ii) above. Notwithstanding any of the foregoing,
the anticipated merger of an Affiliate of Vulcan Energy Corporation with Plains
Resources will not constitute a Change of Control hereunder, and the survivor of
such merger shall remain a party hereto with all rights and obligations
hereunder.

        2.5   Scope of Restricted Business Prohibition. Except as restricted by
this Article II (or by other agreement, including without limitation the LLC
Agreement and the Partnership Agreement), each Plains Entity shall be free to
engage in any business activity whatsoever, including those that may be in
direct competition with any Partnership Entity. For clarity, any owner of equity
interests in Plains Resources may make passive investments in the MLP's
competitors; provided, however, that no such owner (nor any Plains Entity) shall
directly or indirectly use any knowledge or confidential information it received
through the ownership by a Plains Entity of a member interest in the General
Partner or representation on the Board of Directors of the General Partner to
compete, or to engage in or become interested financially in any person that
competes, in a Restricted Business.

        2.6   Enforcement. The Plains Entities agree and acknowledge that the
Partnership Group does not have an adequate remedy at law for the breach by the
Plains Entities of the covenants and agreements set forth in this Article II,
and that any breach by the Plains Entities of the covenants and agreements set
forth in Article II would result in irreparable injury to the Partnership Group.
The Plains Entities further agree and acknowledge that any member of the
Partnership Group may, in addition to the

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other remedies which may be available to the Partnership Group, file a suit in
equity to enjoin the Plains Entities from such breach, and consent to the
issuance of injunctive relief hereunder.

ARTICLE III
Miscellaneous

        3.1   Choice of Law; Submission to Jurisdiction. This Agreement shall be
subject to and governed by the laws of the State of Texas, excluding any
conflicts-of-law rule or principle that might refer the construction or
interpretation of this Agreement to the laws of another state. Each party hereby
submits to the jurisdiction of the state and federal courts in the State of
Texas and to venue in Houston, Harris County, Texas.

        3.2   Notice. All notices or requests or consents provided for or
permitted to be given pursuant to this Agreement must be in writing and must be
given by depositing same in the United States mail, addressed to the Person to
be notified, postpaid, and registered or certified with return receipt requested
or by delivering such notice in person or by telecopier or telegram to such
party. Notice given by personal delivery or mail shall be effective upon actual
receipt. Notice given by telegram or telecopier shall be effective upon actual
receipt if received during the recipient's normal business hours, or at the
beginning of the recipient's next business day after receipt if not received
during the recipient's normal business hours. All notices to be sent to a party
pursuant to this Agreement shall be sent to or made at the address set forth
below such party's signature to this Agreement, or at such other address as such
party may stipulate to the other parties in the manner provided in this
Section 3.2.

        3.3   Entire Agreement; Supersedure. This Agreement constitutes the
entire agreement of the parties relating to the matters contained herein,
superseding all prior contracts or agreements, whether oral or written, relating
to the matters contained herein.

        3.4   Effect of Waiver or Consent. No waiver or consent, express or
implied, by any party to or of any breach or default by any Person in the
performance by such Person of its obligations hereunder shall be deemed or
construed to be a consent or waiver to or of any other breach or default in the
performance by such Person of the same or any other obligations of such Person
hereunder. Failure on the part of a party to complain of any act of any Person
or to declare any Person in default, irrespective of how long such failure
continues, shall not constitute a waiver by such party of its rights hereunder
until the applicable statute of limitations period has run.

        3.5   Amendment or Modification. This Agreement may be amended or
modified from time to time only by the written agreement of all the parties
hereto; provided, however, that the MLP and the OLPs may not, without the prior
approval of the Conflicts Committee, agree to any amendment or modification of
this Agreement that, in the reasonable discretion of the General Partner, will
adversely affect the holders of Common Units. Each such instrument shall be
reduced to writing and shall be designated on its face an "Amendment" or an
"Addendum" to this Agreement.

        3.6   Assignment. No party shall have the right to assign its rights or
obligations under this Agreement without the consent of the other parties
hereto.

        3.7   Counterparts. This Agreement may be executed in any number of
counterparts with the same effect as if all signatory parties had signed the
same document. All counterparts shall be construed together and shall constitute
one and the same instrument.

        3.8   Severability. If any provision of this Agreement or the
application thereof to any Person or circumstance shall be held invalid or
unenforceable to any extent, the remainder of this Agreement and the application
of such provision to other Persons or circumstances shall not be affected
thereby and shall be enforced to the greatest extent permitted by law.

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        3.9   Gender, Parts, Articles and Sections. Whenever the context
requires, the gender of all words used in this Agreement shall include the
masculine, feminine and neuter, and the number of all words shall include the
singular and plural. All references to Article numbers and Section numbers refer
to Parts, Articles and Sections of this Agreement.

        3.10 Further Assurances. In connection with this Agreement and all
transactions contemplated by this Agreement, each signatory party hereto agrees
to execute and deliver such additional documents and instruments and to perform
such additional acts as may be necessary or appropriate to effectuate, carry out
and perform all of the terms, provisions and conditions of this Agreement and
all such transactions.

        3.11 Withholding or Granting of Consent. Each party may, with respect to
any consent or approval that it is entitled to grant pursuant to this Agreement,
grant or withhold such consent or approval in its sole and uncontrolled
discretion, with or without cause, and subject to such conditions as it shall
deem appropriate.

        3.12 U.S. Currency. All sums and amounts payable to or to be payable
pursuant to the provisions of this Agreement shall be payable in coin or
currency of the United States of America that, at the time of payment, is legal
tender for the payment of public and private debts in the United States of
America.

        3.13 Laws and Regulations. Notwithstanding any provision of this
Agreement to the contrary, no party hereto shall be required to take any act, or
fail to take any act, under this Agreement if the effect thereof would be to
cause such party to be in violation of any applicable law, statute, rule or
regulation.

        3.14 Negotiation of Rights of Limited Partners, Assignees, and Third
Parties. The provisions of this Agreement are enforceable solely by the parties
to this Agreement, and no Limited Partner, Assignee or other Person shall have
the right, separate and apart from the MLP or the OLP, to enforce any provision
of this Agreement or to compel any party to this Agreement to comply with the
terms of this Agreement.

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        IN WITNESS WHEREOF, the parties have executed this Agreement on, and
effective as of, the date first written above.

    PLAINS RESOURCES INC.
 
 
By:
 
/s/  JOHN T. RAYMOND      

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Name: John T. Raymond
Title: President and Chief Executive Officer
 
 
Address for Notice:
 
 
700 Milam, Suite 3100
Houston, Texas 77002
Telecopy Number: (713) 654-1523
 
 
PLAINS ALL AMERICAN PIPELINE, L.P.
 
 
By: PLAINS AAP, L.P., its general partner
 
 
By: PLAINS ALL AMERICAN GP LLC, its general partner
 
 
 
 
By:
/s/  HARRY N. PEFANIS      

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Name: Harry N. Pefanis
Title: President
 
 
Address for Notice:     333 Clay Street, Suite 1600
Houston, Texas 77002
Telecopy Number: (713) 646-4313            

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    PLAINS MARKETING, L.P.
 
 
By: PLAINS MARKETING GP INC., its general partner
 
 
 
 
By:
/s/  HARRY N. PEFANIS      

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Name: Harry N. Pefanis
Title: President and Chief Operating Officer
 
 
Address for Notice:
 
 
333 Clay Street, Suite 1600
Houston, Texas 77002
Telecopy Number: (713) 646-4313
 
 
PLAINS PIPELINE, L.P.
 
 
By: PLAINS MARKETING GP INC., its general partner
 
 
 
 
By:
/s/  HARRY N. PEFANIS      

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Name: Harry N. Pefanis
Title: President and Chief Operating Officer
 
 
Address for Notice:
 
 
333 Clay Street, Suite 1600
Houston, Texas 77002
Telecopy Number: (713) 646-4313
 
 
PLAINS ALL AMERICAN GP LLC
 
 
By:
 
/s/  HARRY N. PEFANIS      

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Name: Harry N. Pefanis
Title: President and Chief Operating Officer
 
 
Address for Notice:
 
 
333 Clay Street, Suite 1600
Houston, Texas 77002
Telecopy Number: (713) 646-4313

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QuickLinks

EXHIBIT 10.3

TABLE OF CONTENTS
AMENDED AND RESTATED OMNIBUS AGREEMENT
ARTICLE I Definitions
ARTICLE II Business Opportunities
ARTICLE III Miscellaneous