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                                                                   EXHIBIT 10(o)



                              SECOND AMENDMENT TO
                  THIRD AMENDED AND RESTATED CREDIT AGREEMENT

     THIS SECOND AMENDMENT TO THIRD AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") dated as of the 7th day of March, 1997, by and among PLAINS
RESOURCES INC., a Delaware corporation (the "Company"), ING (U.S.) CAPITAL
CORPORATION, f/k/a Internationale Nederlanden (U.S.) Capital Corporation, as
Agent ("Agent"), and the Lenders under the Original Agreement (as defined
herein).

                              W I T N E S S E T H:

     WHEREAS, the Company, Agent and Lenders entered into that certain Third
Amended and Restated Credit Agreement dated as of April 11, 1996, as amended by
that certain First Amendment to Third Amended and Restated Credit Agreement
dated December 16, 1996 (as amended, the "Original Agreement") for the purposes
and consideration therein expressed, pursuant to which Lenders became obligated
to make and made loans to the Company as therein provided; and

     WHEREAS, the Company, Agent and Lenders desire to amend the Original
Agreement for the purposes described herein;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein and in the Original Agreement, in consideration
of the loans which may hereafter be made by Lenders to the Company, and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto do hereby agree as follows:

                   ARTICLE I. -- Definitions and References

     (S) 1.1.  Terms Defined in the Original Agreement.  Unless the context
otherwise requires or unless otherwise expressly defined herein, the terms
defined in the Original Agreement shall have the same meanings whenever used in
this Amendment.

     (S) 1.2.  Other Defined Terms.  Unless the context otherwise requires, the
following terms when used in this Amendment shall have the meanings assigned to
them in this (S) 1.2.

          "Amendment" means this Second Amendment to Third Amended and Restated
     Credit Agreement.

          "Amendment Documents" means this Amendment, the Renewal Notes, and the
     Mortgage Amendments described in Section 3.1(iv)(A) hereof.

          "Credit Agreement" means the Original Agreement as amended hereby.

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          "Original Notes" means the "Notes" referred to and defined as such in
     the Original Agreement.

          "Renewal Notes" has the meaning given it in Section 3.1(iii).

                           ARTICLE II. -- Amendments

     (S) 2.1   Definitions.  The definitions of "Commitment", "Majority
Lenders", "Percentage Share", "Quarterly Date" and "Revolving Credit Termination
Date" set forth in Section 1.01 of the Original Agreement are hereby amended in
their entirety to read as follows:

          "Commitment" shall mean the obligation of Lenders to make Loans in an
     aggregate amount at any one time outstanding up to but not exceeding
     $165,000,000, as the same may be reduced at any time or from time to time
     pursuant to Sections 2.03(a), (b) or (c).

          "Majority Lenders" shall mean Lenders having Percentage Shares equal
     to sixty-six and two-thirds percent (66 2/3%).

          "Percentage Share" shall mean, with respect to any Lender (a) when
     used in Section 2.01 or when no Loans are outstanding hereunder, the
     percentage set forth opposite such Lender's name on the Lender Schedule
     attached to this Agreement, as from time to time amended or supplemented,
     or with respect to a Person who shall become a Lender after the date of
     this Agreement, the percentage of the Commitment and Loans assigned to and
     assumed by such Lender, as set forth in the assignment made pursuant to
     Section 11.06(b), and (b) when used otherwise, the percentage equal to the
     unpaid principal balance of such Lender's Loans at the time in question
     divided by the aggregate unpaid principal balance of all Loans at such
     time.

          "Quarterly Dates" shall mean the first Business Day of April, July,
     October and January in each year, the first of which shall be April 1,
     1997.

          "Revolving Credit Termination Date" shall mean the earlier of (a) July
     1, 1999 and (b) the date on which the Commitment is reduced to zero or
     terminated pursuant to Section 2.03 hereof.

     (S) 2.2   Commitment Fee.  The reference to "a rate per annum equal to one-
half of one percent (0.5%)" in the first sentence of Section 2.04(a) of the
Original Agreement is hereby amended to refer instead to "a rate per annum equal
to three-eighths of one percent (0.375%)".

     (S) 2.3   Repayment of Term Loans.  Section 3.01(b) of the Original
Agreement is hereby amended in its entirety to read as follows:

          (b) The Company will repay the principal of the Term Loans in twenty
     installments payable on each Quarterly Date beginning October 1, 1999, with
     the final installment being due and payable on or before July 1, 2004.
     Each such installment shall 

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     be equal to one-twentieth of the original principal amount of the Term
     Loans as of the Revolving Credit Termination Date. In any event all unpaid
     principal and interest shall be due and payable in full on the final
     maturity of July 1, 2004. As set forth in Section 2.07(c), all optional and
     mandatory prepayments made on the Term Loans shall be applied to the
     scheduled installments in inverse order of their maturity.

     (S) 2.4.  Indebtedness.  Section 8.09(a) of the Original Agreement is
hereby amended in its entirety to read as follows:

          (a) the Obligations;

     (S) 2.5.  Amendments.  Section 11.04 of the Original Agreement is hereby
amended in its entirety to read as follows:

          11.04  Amendments, Etc.  No amendment, modification or waiver of any
     provision of this Agreement shall be valid or effective against any party
     hereto unless the same is in writing and signed by (a) if such party is the
     Company, by the Company, (b) if such party is Agent, by Agent, and (c) if
     such party is a Lender, by Majority Lenders; provided, notwithstanding the
     foregoing or anything to the contrary herein, no such amendment,
     modification or waiver shall be valid or effective against any Lender
     (unless signed by such Lender) which would:  (i) increase the Commitment of
     such Lender or subject such Lender to any additional obligations, (ii)
     reduce any fees hereunder, or the principal of, or interest on, such
     Lender's Note, (iii) postpone any date fixed for any payment of any such
     fees, principal or interest, (iv) amend the definition herein of "Majority
     Lenders" or otherwise change the aggregate amount of Percentage Shares
     which is required for Agent, Lenders or any of them to take any particular
     action under the Loan Documents, or (v) release the Company from its
     obligation to pay such Lender's Note or any Guarantor from its guaranty of
     such payment; provided, further, in clarification of the foregoing,
     Majority Lenders may increase the aggregate Commitment of all Lenders
     (pursuant to an increase in such Majority Lenders' individual Commitments),
     provided that no individual Lender's Commitment may be increased in
     connection with any such increase in the aggregate Commitment without such
     individual Lender's consent as set forth in clause (i) above.

     (S) 2.6.  Lender Schedule.  The Original Agreement is hereby amended by
adding a Lender Schedule immediately following the signature pages thereof in
the form of the Lender Schedule attached hereto.

     (S) 2.7.  Borrowing Base.  Lenders hereby designate the Borrowing Base as
$165,000,000, effective for the period beginning on the date hereof, and
continuing until but not including the next date as of which the Borrowing Base
is redetermined.

     (S) 2.8.  Florida Mortgaged Property.  Each Lender hereby acknowledges and
agrees that at the request of Borrower the Sixth Amendment to Deed of Trust,
Mortgage, Assignment, Security Agreement, Financing Statement and Fixture Filing
described in Section 3.1(iv)(A)(i) hereof provides that the indebtedness secured
by properties located in the State of Florida shall be limited to the amount of
$125,000,000.

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                  ARTICLE III. -- Conditions of Effectiveness

     (S) 3.1.  Effective Date.  This Amendment shall become effective as of the
date first above written when and only when (i) Agent shall have received, at
Agent's office, a counterpart of this Amendment executed and delivered by the
Company and each Lender, (ii) the Company shall have paid to Agent for the
account of each Lender according to its Percentage Share a facility increase fee
in the aggregate amount of $100,000, (iii) the Company shall have issued and
delivered to each Lender a promissory note with appropriate insertions in the
form attached hereto as Exhibit A payable to the order of such Lender on or
before July 1, 2004 (collectively, the "Renewal Notes"), duly executed on behalf
of the Company, dated the date hereof, and expressly renewing, extending and
increasing, but not novating or extinguishing, such Lender's Original Note, and
(iv) Agent shall have additionally received all of the following documents, each
document (unless otherwise indicated) being dated the date of receipt thereof by
Agent, duly authorized, executed and delivered, and in form and substance
satisfactory to Agent:

          (A) Mortgage Amendments.  (i) That certain Sixth Amendment to Deed of
     Trust, Mortgage, Assignment, Security Agreement, Financing Statement and
     Fixture Filing of even date herewith by Calumet, Stocker, the Company and
     Agent, for the benefit of Lenders, amending that certain Deed of Trust,
     Mortgage, Assignment, Security Agreement and Fixture Filing dated February
     11, 1994 by Calumet Florida, Inc., Stocker Resources, L.P., the Company and
     Plains Resources Utah Inc. in favor of Agent for the benefit of Lenders, as
     heretofore amended, and (ii) that certain Second Amendment to Mortgage,
     Assignment, Security Agreement, Financing Statement and Fixture Filing of
     even date herewith by Plains Illinois and Agent, for the benefit of
     Lenders, amending that certain Mortgage, Assignment, Security Agreement and
     Fixture Filing dated March 19, 1996 by Plains Illinois Inc. in favor of
     Agent for the benefit of Lenders, as heretofore amended.

          (B) Opinions of Counsel for the Company.  A written opinion of (I)
     Michael Patterson, Esq., counsel for the Company, dated as of the date of
     this Amendment, addressed to Agent and Lenders, to the effect that the
     Amendment Documents have been duly authorized, executed and delivered by
     the Company and the Subsidiary Guarantors, and (II) Fulbright & Jaworski,
     L.L.P., counsel for the Company, dated as of the date of this Amendment,
     addressed to Agent and Lenders, to the effect that the Credit Agreement and
     the Notes constitute the legal, valid and binding obligations of the
     Company, enforceable in accordance with their terms (subject, as to
     enforcement of remedies, to applicable bankruptcy, reorganization,
     insolvency and similar laws and to general principles of equity) and that
     the New York choice of law provisions contained therein are enforceable
     under Texas law.

          (C) Officer's Certificate.  A certificate of a duly authorized officer
     of the Company to the effect that all of the representations and warranties
     set forth in Article IV hereof are true and correct at and as of the date
     thereof.

          (D) Supporting Documents.  (I) A certificate of the Secretary of the
     Company dated the date of this Amendment certifying that attached thereto
     is a true and complete 

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     copy of resolutions adopted by the Board of Directors of the Company
     authorizing the execution, delivery and performance of the Amendment
     Documents and certifying the names and true signatures of the officers of
     the Company authorized to sign the Amendment Documents and (II) such
     supporting documents as Agent may reasonably request.

                 ARTICLE IV. -- Representations and Warranties

     (S) 4.1.  Representations and Warranties of the Company.  In order to
induce Agent and Lenders to enter into this Amendment, the Company represents
and warrants to Agent and Lenders that:

          (a) The representations and warranties contained in Section 7 of the
     Original Agreement, are true and correct at and as of the time of the
     effectiveness hereof, subject to the amendment of certain of the Schedules
     to the Credit Agreement as attached hereto.

          (b) The Company and the Subsidiaries are duly authorized to execute
     and deliver this Amendment and the other Amendment Documents to the extent
     a party thereto, and the Company is and will continue to be duly authorized
     to borrow and perform its obligations under the Credit Agreement.  The
     Company and the Subsidiaries have duly taken all corporate action necessary
     to authorize the execution and delivery of this Amendment and the other
     Amendment Documents, to the extent a party thereto, and to authorize the
     performance of their respective obligations thereunder.

          (c) The execution and delivery by the Company and the Subsidiaries of
     this Amendment and the other Amendment Documents, to the extent a party
     thereto, the performance by the Company and the Subsidiaries of their
     respective obligations hereunder and thereunder, and the consummation of
     the transactions contemplated hereby and thereby, do not and will not
     conflict with any provision of law, statute, rule or regulation or of the
     certificate or articles of incorporation and bylaws of the Company or any
     Subsidiary, or of any material agreement, judgment, license, order or
     permit applicable to or binding upon the Company or any Subsidiary, or
     result in the creation of any lien, charge or encumbrance upon any assets
     or properties of the Company or any Subsidiary, except in favor of Agent
     for the benefit of Lenders.  Except for those which have been duly
     obtained, no consent, approval, authorization or order of any court or
     governmental authority or third party is required in connection with the
     execution and delivery by the Company or any Subsidiary of this Amendment
     or any other Amendment Document, to the extent a party thereto, or to
     consummate the transactions contemplated hereby and thereby.

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          (d) When this Amendment and the other Amendment Documents have been
     duly executed and delivered, each of the Basic Documents, as amended by
     this Amendment and the other Amendment Documents, will be a legal and
     binding instrument and agreement of the Company and the Subsidiaries, to
     the extent a party thereto, enforceable in accordance with its terms,
     (subject, as to enforcement of remedies, to applicable bankruptcy,
     insolvency and similar laws applicable to creditors' rights generally and
     to general principles of equity).

                          ARTICLE V. -- Miscellaneous

     (S) 5.1.  Ratification of Agreements.  The Original Agreement, as hereby
amended, is hereby ratified and confirmed in all respects.  The Basic Documents,
as they may be amended or affected by this Amendment and/or the other Amendment
Documents, are hereby ratified and confirmed in all respects.  Any reference to
the Credit Agreement in any Basic Document shall be deemed to refer to this
Amendment also.  The execution, delivery and effectiveness of this Amendment and
the other Amendment Documents shall not, except as expressly provided herein or
therein, operate as a waiver of any right, power or remedy of Agent or any
Lender under the Credit Agreement or any other Basic Document nor constitute a
waiver of any provision of the Credit Agreement or any other Basic Document.

     (S) 5.2.  Ratification of Security Documents.  The Company, Agent and
Lenders each acknowledge and agree that any and all indebtedness, liabilities or
obligations arising under or in connection with the Notes are Obligations and is
secured indebtedness under, and is secured by, each and every Security Document
to which the Company is a party.  The Company hereby re-pledges, re-grants and
re-assigns a security interest in and lien on every asset of the Company
described as collateral in any Security Document.

     (S) 5.3.  Survival of Agreements.  All representations, warranties,
covenants and agreements of the Company herein and in the other Amendment
Documents shall survive the execution and delivery of this Amendment and the
other Amendment Documents and the performance hereof and thereof, including
without limitation the making or granting of each Loan, and shall further
survive until all of the Obligations are paid in full.  All statements and
agreements contained in any certificate or instrument delivered by the Company
or any Subsidiary hereunder, under the other Amendment Documents or under the
Credit Agreement to Agent or any Lender shall be deemed to constitute
representations and warranties by, or agreements and covenants of, the Company
under this Amendment and under the Credit Agreement.

     (S) 5.4.  Basic Documents.  This Amendment and each of the other Amendment
Documents is a Basic Document, and all provisions in the Credit Agreement
pertaining to Basic Documents apply hereto and thereto.

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     (S) 5.5.  GOVERNING LAW.  THIS AMENDMENT AND THE OTHER AMENDMENT DOCUMENTS
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
NEW YORK AND ANY APPLICABLE LAWS OF THE UNITED STATES OF AMERICA IN ALL
RESPECTS, INCLUDING CONSTRUCTION, VALIDITY AND PERFORMANCE.

     (S) 5.6.  Counterparts.  This Amendment and each of the other Amendment
Documents may be separately executed in counterparts and by the different
parties hereto in separate counterparts, each of which when so executed shall be
deemed to constitute one and the same Amendment or Amendment Document, as the
case may be.

     IN WITNESS WHEREOF, this Amendment is executed as of the date first above
written.


                              PLAINS RESOURCES INC.


                              By:/s/ Phillip D. Kramer
                                 ------------------------------------------
                                 Phillip D. Kramer
                                 Vice President and Chief Financial Officer


                              ING (U.S.) CAPITAL CORPORATION,
                              f/k/a Internationale Nederlanden (U.S.) Capital
                              Corporation, individually as a Lender and as
                              Agent


                              By: /s/ Christopher R. Wagner
                                 ------------------------------------------
                                 Christopher R. Wagner, Vice President


                              THE FIRST NATIONAL BANK OF BOSTON, Lender


                              By: /s/ Christopher Holmgren
                                 ------------------------------------------
                                 Name: Christopher Holmgren
                                 Title:    Director

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                              DEN NORSKE BANK ASA, Lender



                              By:  /s/ Byron L. Cooley
                                 -----------------------------------------
                                 Name Byron L. Cooley
                                 Title: Senior Vice President


                              By:  /s/ Morten Bjornsen
                                 -----------------------------------------
                                 Name: Morten Bjornsen
                                 Title: Senior Vice President


                              WELLS FARGO BANK (TEXAS),
                              NATIONAL ASSOCIATION
                              (f/k/a First Interstate Bank of Texas, N.A.),
                              Lender


                              By:  /s/ Ann M. Rhoads
                                 ------------------------------------------
                                 Ann M. Rhoads, Vice President


                              TEXAS COMMERCE BANK NATIONAL 
                              ASSOCIATION, Lender


                              By: /s/ Scott H. Richardson
                                 --------------------------------------------
                                 Name: Scott H. Richardson
                                 Title: Vice President


                              COMERICA BANK-TEXAS, Lender


                              By:  /s/ James Kimble
                                 -------------------------------------------
                                 Name:James Kimble
                                 Title:  Energy Banking Officer

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                             CONSENT AND AGREEMENT

     Each of the undersigned Subsidiary Guarantors hereby consents to the
provisions of this Amendment and the transactions contemplated herein and hereby
(i) acknowledges and agrees that any and all indebtedness, liabilities or
obligations arising under or in connection with the Notes are Obligations and
are secured indebtedness under, and are secured by, each and every Security
Document to which it is a party, (ii) re-pledges, re-grants and re-assigns a
security interest in and lien on all of its assets described as collateral in
any Security Document, (iii) ratifies and confirms its Amended and Restated
Guaranty dated April 11, 1996 made by it for the benefit of Agent and Lenders,
and (iv) expressly acknowledges and agrees that such Subsidiary Guarantor
guarantees all indebtedness, liabilities and obligations arising under or in
connection with the Notes pursuant to the terms of such Amended and Restated
Guaranty, and agrees that its obligations and covenants thereunder are
unimpaired hereby and shall remain in full force and effect.  Each of the
undersigned hereby further agrees that any obligation of the Company arising
pursuant to Section 2.10 of the Credit Agreement shall constitute "Obligations"
under the Guaranty.

                         PLAINS MARKETING & TRANSPORTATION INC.
                         PLAINS RESOURCES INTERNATIONAL INC.
                         PLAINS TERMINAL & TRANSFER CORPORATION
                         PLX CRUDE LINES INC.
                         STOCKER RESOURCES, INC.
                         PLX INGLESIDE INC.
                         CALUMET FLORIDA, INC.
                         PLAINS ILLINOIS INC.


                         By: /s/ Phillip D. Kramer
                            ---------------------------------------------
                            Phillip D. Kramer, Vice President


                         STOCKER RESOURCES, L.P.

                         By:  Stocker Resources, Inc.,
                               its General Partner


                         By:   /s/ Phillip D. Kramer
                            --------------------------------------------
                               Phillip D. Kramer, Vice President

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