<PAGE>   1
                                                                    EXHIBIT 10.8

                               SERVICES AGREEMENT

                  THIS SERVICES AGREEMENT is entered into on, and effective as
of, July 1, 2000 (the "Effective Date") by and between DIAMOND SHAMROCK REFINING
AND MARKETING COMPANY, a Delaware corporation ("DSRMC") and certain of its
affiliates listed on Exhibit A attached hereto (hereinafter referred to
collectively as "Diamond"), SHAMROCK LOGISTICS, L.P. ("Master Partnership"),
SHAMROCK LOGISTICS OPERATIONS, L.P. ("Operating Partnership"), and their general
partner RIVERWALK LOGISTICS, L.P. ("General Partner Partnership"), all Delaware
limited partnerships (collectively, the "Partnership Entities"), and Riverwalk
Logistics, L.P.'s general partner, SHAMROCK LOGISTICS GP, LLC ("General
Partner"). The Partnership Entities and the General Partner will sometimes be
referred to herein as the "Entities".

                                    RECITALS:

                  WHEREAS, the General Partner, as the general partner of the
General Partner Partnership, manages all activities of the Partnership Entities;

                  WHEREAS, DSRMC and certain of DSRMC's Affiliates, on behalf of
the General Partner, will provide certain services to the Entities, for which
they will be compensated as provided herein; and

                  WHEREAS, Diamond and the Entities desire by their execution of
this Agreement to evidence their understanding concerning the provision of those
services by Diamond to the Entities;

                  THEREFORE, 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:



                                      -1-
<PAGE>   2

                  1. Services.

                  (i) Corporate, General, and Administrative Services. During
the term of this Agreement, in exchange for a fee set forth in Section 4(i)
herein, Diamond agrees to provide to the Entities the services set forth on
Exhibit B hereto (the "Corporate, General, and Administrative Services") as an
incidental part of its ongoing operations.

                  (ii) Other Services. In addition, during the term of this
Agreement, in exchange for reimbursement as set forth in Section 4(ii) herein,
Diamond agrees to provide to the Entities the services and personnel necessary
to operate and maintain the Entities to the extent such activities and services
would not otherwise have been retained or occurred as an incidental part of
Diamond's ongoing operations, such services and personnel to include but not
limited to those relating to the items set forth on Exhibit C hereto (the "Other
Services" and, together with the Corporate, General, and Administrative
Services, the "Services").

                  (iii) Use of Third-Party Service Providers. Diamond may cause
one or more third party contractors to provide any Service (with any Service so
provided by a third party contractor being referred to herein as an "Outsourced
Service"); provided, however, that (a) any Outsourced Service provided solely
for the benefit of the Entities shall require approval by the General Partner
Partnership, and (b) any Outsourced Services shall be subject to the provisions
of this Agreement the same way a Service is subject to the provisions of this
Agreement. If, from time to time, Diamond determines to publish a Request for
Proposal for a third party to provide as Outsourced Services any one or more of
the Services then being provided under this Agreement, Diamond shall give the
Entities at least ten days prior written notice of such decision and shall
promptly advise the Entities of the terms of any winning bid. The Entities shall
hold confidential the terms of any proposal disclosed to them pursuant to the
foregoing sentence. The Entities shall advise Diamond in writing within seven
business days after receipt of notice of the terms whether or not the Entities
desire to participate in the Outsourced Services at the level of service set out
in the winning bid (the "Agreed Level of Service") and, in the case of an



                                      -2-
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Outsourced Service provided solely for the benefit of the Entities, whether the
General Partner Partnership, on behalf of the Entities, has approved the
contractor and the terms and conditions of such Outsourced Service. In the event
the Entities decide to terminate such Outsourced Service, it shall be terminated
effective as of the effective date of the new contract between Diamond and the
third party providing the Service. If the Entities desire to continue to be
provided with such Outsourced Service, they shall be obligated to reimburse
Diamond for their allocable portion of the costs incurred by Diamond under the
agreement between Diamond and the third party provider of the Outsourced Service
(up to the Agreed Level of Service). The Entities may not terminate any such
Outsourced Service except upon proper notice as provided in the agreement for
such Outsourced Service. No agreement entered into by Diamond after the
Effective Date shall give to any third party a preferential right to provide the
Entities with services following the expiration of this Agreement.

                  2. Cancellation or Reduction of Services.

                  Except as provided below in this Section 2, the Entities may
terminate or reduce the level of any Other Service on thirty (30) days' prior
written notice to Diamond. Should the Entities terminate any Other Service being
provided hereunder, Diamond shall have no liability to the Entities for the
Entities' failure or inability to replace such terminated Other Services except
in the form of a downward adjustment required to Direct Charges pursuant to
Section 4(ii). Further, if the Entities terminate any Other Service, the
Entities agree that Diamond shall not be required to provide the terminated
Other Service to the Entities in the future.

                  3. Nature/Quality of Services. The nature and quality of the
Services shall be substantially identical to those provided to other
subsidiaries and affiliates of DSRMC. Diamond alone may determine whether or not
to outsource a Service; provided, however, that in the case of an Outsourced
Service provided solely for the benefit of the Entities the selection of the
contractor and the terms and conditions of the agreement shall be subject to the
approval of the



                                      -3-
<PAGE>   4

General Partner Partnership. Outsourced Services will be of the nature and
quality provided in the agreement with the third party provider.

                  4. Payment.

                  (i) Corporate, General, and Administrative Services. In
         consideration of the Corporate, General, and Administrative Services,
         the General Partner Partnership shall pay DSRMC $5,200,000 annually
         (the "Administrative Fee"), which amount shall be paid in twelve equal
         monthly installments in arrears, the first such payment being made with
         respect to the month ended July 31, 2000; provided, however, that the
         Administrative Fee may be increased at the request of Diamond and
         subject to the approval and consent of the Audit Committee of the
         General Partner, as follows:

                           (a) for each year during the term of this agreement,
         beginning with the year that starts on the first anniversary of the
         Effective Date, up to 1.5% per year and an additional percentage not to
         exceed the percentage increase in the Consumer Price Index for Urban
         Wage Earners and Clerical published by the United States Department of
         Labor Bureau of Labor Statistics for the preceding calendar year; and

                           (b) in connection with expansions of the Operating
         Partnership's operations through acquisition or construction of new
         assets that require additional Corporate, General, and Administrative
         Services.

                  The Administrative Fee shall be decreased on a pro rata basis
         if one or more of the Corporate, General, and Administrative Services
         are for any reason no longer provided under this Agreement, whether on
         a temporary or permanent basis, for such time as such Services are not
         provided.

                  (ii) Other Services. In consideration of the Other Services,
         the General Partner Partnership shall reimburse Diamond for (i) all
         out-of-pocket expenses incurred by Diamond exclusively to provide the
         Other Services to the Entities, (ii) the actual cost of any item
         purchased exclusively for the use of the Entities by Diamond, and (iii)
         all



                                      -4-
<PAGE>   5

         expenses actually incurred by Diamond for Outsourced Services and
         allocable to the Entities consistent with Section 1 (iii) of this
         Agreement (the amounts referred to in (i), (ii), and (iii) being
         collectively referred to as the "Direct Charges"); provided, however,
         that in no event shall Direct Charges include expenses or costs
         incurred for the provision of Corporate, General, and Administrative
         Services, and provided further that the General Partner Partnership
         shall not be invoiced for or required to pay Direct Charges in
         connection with an Other Service that is not being provided under this
         Agreement for any reason, whether on a temporary or permanent basis,
         for such time as such Services are not provided.

                  (iii) Taxes. If the compensation for the Services does not
         include sales, use, excise, value added or similar taxes, and if any
         such taxes are imposed on the Services, the General Partner shall pay
         or reimburse Diamond for any such taxes.

                  5. Invoicing for Direct Charges.

                  (i) Diamond shall invoice, or cause its affiliates to invoice,
         the General Partner Partnership by the 30th working day of each month
         for all Direct Charges with respect to the preceding month and any
         adjustments that may be necessary to correct prior invoices. All
         invoices shall reflect in reasonable detail a description of the Other
         Services performed during the preceding month, and shall be due and
         payable on the last day of the month of the invoice. In the event of
         default in payment by the General Partner Partnership, upon thirty (30)
         days= written notice to the General Partner Partnership, delivered as
         provided below, Diamond may terminate this Agreement as to those
         Services which relate to the unpaid portion of the invoice if it has
         not received payment within such thirty (30) days. In the event of a
         dispute as to the propriety of invoiced amounts (a "Dispute"), the
         General Partner Partnership shall pay all undisputed amounts on each
         invoice, but shall be entitled to withhold payment of any amount in
         dispute and shall notify Diamond within ten (10) business days from
         receipt of the



                                      -5-
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         disputed invoice of the disputed amount and the reasons each such
         charge is disputed. Diamond shall provide the General Partner
         Partnership with records relating to the disputed amount so as to
         enable the parties to resolve the Dispute. If the Dispute cannot be
         resolved within fifteen (15) days of Diamond's receiving such
         notification, any party may initiate arbitration proceedings in the
         manner provided for by Section 5(iii). So long as the parties are
         attempting in good faith to resolve the Dispute, Diamond shall not be
         entitled to terminate the Services related to and by reason of the
         disputed charge.

                  (ii) Any statement or payment not disputed in writing by
         either party within one year of the date of such statement or payment
         shall be considered final and no longer subject to adjustment. The
         General Partner Partnership shall not be obligated to pay for any
         Direct Charges for which statements for payment are submitted more than
         one year after the termination of this Agreement.

                  (iii) Resolution of Disputes shall be exclusively governed by
         and settled in accordance with the provisions of this Section 5(iii);
         provided however, that nothing contained herein shall preclude any
         party from seeking or obtaining (i) injunctive relief or (ii) equitable
         or other judicial relief, in each case to preserve the status quo,
         pending resolution of Disputes hereunder. DSRMC or any of the Entities
         may commence proceedings hereunder by delivering written notice to the
         other party expressly requesting arbitration hereunder after a Dispute
         has remained unresolved for the period of time specified under Section
         5(i) hereof. The parties hereby agree to submit all Disputes to
         arbitration hereunder, which arbitration shall be final, conclusive,
         and binding upon the parties, their successors and assigns. The
         arbitration shall be conducted in San Antonio, Texas by a sole
         arbitrator selected by mutual agreement of the parties not later than
         ten (10) days after delivery of such notice, or, failing such
         agreement, appointed pursuant to the commercial arbitration rules of
         the American Arbitration Association, as amended from time to time
         ("AAA Rules"). The arbitrators shall be generally knowledgeable



                                      -6-
<PAGE>   7
         about the pipeline and terminal operating industry and the nature of
         the issues to be arbitrated and shall be qualified by education,
         experience, and training to render a decision upon the issues to be
         arbitrated. If the arbitrator selected becomes unable to serve, his or
         her successor shall be similarly selected or appointed. The arbitration
         shall be conducted in accordance with the AAA Rules to the extent such
         rules do not conflict with the terms of this agreement. Notwithstanding
         the foregoing: (i) each party shall have the right to audit the books
         and records of any other party that are reasonably related to a
         Dispute; (ii) each party shall provide to the other parties involved in
         a Dispute, reasonably in advance of any hearing, copies of all
         documents which such party intends to present at such hearing; and
         (iii) each party shall be allowed to conduct reasonable discovery
         through written requests for information, document requests, requests
         for stipulation of fact, and depositions, the nature and extent of
         which discovery shall be determined by the arbitrator, taking into
         account the needs of the parties and the desirability of making
         discovery expeditious and cost effective. All hearings shall be
         conducted on an expedited schedule, and all proceedings shall be
         confidential. Any party may at its, expense, make a stenographic record
         thereof. The arbitrator shall complete all hearings not later than
         sixty days after his or her selection or appointment and shall make a
         final award not later than thirty days thereafter. All claims presented
         for arbitration shall be particularly identified, and the parties to
         the arbitration shall each prepare a written statement of their
         position and their proposed course of action. These written statements
         of positions and proposed courses of action shall be submitted to the
         arbitrator. In making his or her decision, the arbitrator must accept
         in its entirety the position of one party or the other and make an
         arbitration award based on that party's proposed course of action. The
         arbitrator shall not be empowered in reaching his or her decision to
         equitably adjust the scope of the written statements. All costs and
         expenses of arbitration, including the fees and expenses of the
         arbitrator or of any experts, shall be



                                      -7-
<PAGE>   8

         borne equally between the prevailing and non-prevailing party, except
         that each party shall pay all of its respective attorney's fees,
         consultant's fees, and other costs of participating in the Arbitration
         proceeding. Notwithstanding the foregoing, in no event may the
         arbitrator award multiple, punitive, or exemplary damages. Any
         arbitration award shall be binding and enforceable against each party
         involved in the Dispute and judgment may be entered thereon in any
         court of competent jurisdiction. Payment of any such award shall be
         make within five (5) business days of the arbitrator's decision.

                  6. Input from Entities. Any input necessary for Diamond or any
third party provider to perform any Services shall be submitted by the Entities
in a manner consistent with the practices utilized during the one year period
prior to the Effective Date, which manner shall not be altered except by mutual
written agreement of the parties. Should the Entities' failure to supply such
input render performance of any Services by or on behalf of Diamond unreasonably
difficult, Diamond, upon reasonable notice, may provide a lesser quality of
Services or refuse to perform such Services.

                  7. Entities are Sole Beneficiaries. The Entities acknowledge
that the Services shall be provided only with respect to their business as
currently operated or as mutually agreed by the parties hereto. The Entities
shall not request performance of any Services for the benefit of any entity
other than themselves. The Entities represent and agree that they will use the
Services only in accordance with all applicable federal, state, and local laws
and regulations and communications and common carrier tariffs, and in accordance
with the reasonable conditions, rules, regulations, and specifications which may
be set forth in any manuals, materials, documents, or instructions furnished
from time to time by Diamond to the Entities. Diamond reserves the right to take
all actions, including termination of any Services, that Diamond reasonably
believes to be necessary to assure compliance with applicable laws, regulations,
and tariffs. Diamond will notify the Entities of the reasons for any such
termination of Services.



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                  8. LIMITED WARRANTY, LIMITATION OF LIABILITY.

                  Diamond represents that it will provide or cause the Services
to be provided to the Entities with reasonable care and in accordance with all
applicable laws, rules, and regulations, including without limitation those of
the Federal Energy Regulatory Commission. EXCEPT AS SET FORTH IN THE IMMEDIATELY
PRECEDING SENTENCE AND IN SECTION 3, ALL PRODUCTS OBTAINED FOR THE ENTITIES ARE
AS IS, WHERE IS, WITH ALL FAULTS. DIAMOND MAKES NO (AND HEREBY DISCLAIMS AND
NEGATES ANY AND ALL) REPRESENTATIONS AND WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
WITH RESPECT TO THE SERVICES RENDERED OR PRODUCTS OBTAINED FOR THE ENTITIES.
FURTHERMORE, THE ENTITIES MAY NOT RELY UPON ANY REPRESENTATION OR WARRANTY,
EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE MADE TO DIAMOND BY ANY PARTY (INCLUDING, AN AFFILIATE OF
DIAMOND) PERFORMING SERVICES ON BEHALF ON DIAMOND HEREUNDER, UNLESS SUCH PARTY
MAKES AN EXPRESS WARRANTY TO THE GENERAL PARTNER OR THE PARTNERSHIP ENTITIES.
HOWEVER, IN THE CASE OF OUTSOURCED SERVICES PROVIDED SOLELY FOR THE ENTITIES, IF
THE THIRD PARTY PROVIDER OF SUCH SERVICES MAKES AN EXPRESS WARRANTY, THE
ENTITIES ARE ENTITLED TO CAUSE DIAMOND TO RELY ON SUCH WARRANTY.

                  IT IS EXPRESSLY UNDERSTOOD BY THE ENTITIES THAT DIAMOND AND
ITS AFFILIATES SHALL HAVE NO LIABILITY FOR THE FAILURE OF THIRD PARTY PROVIDERS
TO PERFORM ANY SERVICES HEREUNDER AND FURTHER THAT DIAMOND AND ITS AFFILIATES
SHALL HAVE NO LIABILITY WHATSOEVER FOR THE SERVICES PROVIDED BY ANY SUCH THIRD
PARTY UNLESS SUCH SERVICES ARE PROVIDED IN A MANNER WHICH WOULD EVIDENCE GROSS



                                      -9-
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NEGLIGENCE OR INTENTIONAL MISCONDUCT ON THE PART OF DSRMC OR ITS AFFILIATES. THE
ENTITIES AGREE THAT THE REMUNERATION PAID TO DIAMOND HEREUNDER FOR THE SERVICES
TO BE PERFORMED REFLECT THIS LIMITATION OF LIABILITY AND DISCLAIMER OF
WARRANTIES. IN NO EVENT SHALL DIAMOND BE LIABLE TO THE ENTITIES OR ANY OTHER
PERSON FOR ANY INDIRECT, SPECIAL, OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY
ERROR IN THE PERFORMANCE OF SERVICES OR FROM THE BREACH OF THIS AGREEMENT,
REGARDLESS OF THE FAULT OF DIAMOND, ANY DIAMOND AFFILIATE, OR ANY THIRD PARTY
PROVIDER OR WHETHER DIAMOND, ANY DIAMOND AFFILIATE, OR THE THIRD PARTY PROVIDER
ARE WHOLLY, CONCURRENTLY, PARTIALLY, OR SOLELY NEGLIGENT. TO THE EXTENT ANY
THIRD PARTY PROVIDER HAS LIMITED ITS LIABILITY TO DIAMOND OR ITS AFFILIATE FOR
SERVICES UNDER AN OUTSOURCING OR OTHER AGREEMENT, THE ENTITIES AGREE TO BE BOUND
BY SUCH LIMITATION OF LIABILITY FOR ANY PRODUCT OR SERVICE PROVIDED TO THE
ENTITIES BY SUCH THIRD PARTY PROVIDER UNDER DIAMOND'S OR SUCH AFFILIATE'S
AGREEMENT.

                  9. FORCE MAJEURE.

                  DIAMOND SHALL HAVE NO OBLIGATION TO PERFORM OR CAUSE THE
SERVICES TO BE PERFORMED IF ITS FAILURE TO DO SO IS CAUSED BY OR RESULTS FROM
ANY ACT OF GOD, GOVERNMENTAL ACTION, NATURAL DISASTER, STRIKE, FAILURE OF
ESSENTIAL EQUIPMENT OR ANY OTHER CAUSE OR CIRCUMSTANCE BEYOND THE REASONABLE
CONTROL OF DIAMOND, OR, IF APPLICABLE, ITS AFFILIATES OR THIRD PARTY PROVIDERS
OF SERVICES TO DIAMOND ("EVENT OF FORCE MAJEURE"). DIAMOND WILL NOTIFY THE
ENTITIES OF ANY EVENT OF FORCE MAJEURE. DIAMOND AGREES THAT UPON RESTORING THE
SERVICE FOLLOWING ANY EVENT OF FORCE MAJEURE, DIAMOND WILL



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ALLOW THE ENTITIES TO HAVE EQUAL PRIORITY WITH DIAMOND AND ITS AFFILIATES, IN
ACCORDANCE WITH PRIOR PRACTICE, WITH RESPECT TO ACCESS TO THE RESTORED SERVICE.

                  10. Severability.

                  In the event any portion of this Agreement shall be found by a
court of competent jurisdiction to be unenforceable, that portion of the
Agreement will be null and void and the remainder of the Agreement will be
binding on the parties as if the unenforceable provisions had never been
contained herein.

                  11. Assignment.

                  Except for the ability of Diamond to cause one or more of the
Services to be performed by a third party provider (subject to the terms of this
Agreement), no party shall have the right to assign its rights or obligations
under this Agreement without the consent of the other party.

                  12. Entire Agreement, Supersedure.

                  This Agreement constitutes the entire agreement of the parties
relating to the performance of the Services; all prior or contemporaneous
written or oral agreements are merged herein; this Agreement may not be changed
except by a writing signed by both parties.

                  13. Choice of Law.

                  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.

                  14. Amendment or Modification.

                  This Agreement may be amended or modified from time to time
only by a written amendment signed by the Entities and Diamond; provided however
that the Master Partnership and the Operating Partnership may not, without the
prior approval of the Audit Committee of the Master Partnership, agree to any
amendment or modification of this Agreement that, in the



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reasonable discretion of the General Partner Partnership, will adversely affect
the Holders of the Common Units.

                  15. Notices.

                  Any notice, request, instruction, correspondence or other
document to be given hereunder by either party to the other (herein collectively
called "Notice") shall be in writing and delivered personally or mailed, postage
prepaid, or by telegram or telecopier, as follows:

                           If to Diamond:

                           Diamond Shamrock Refining and Marketing Company
                           P.O. Box 696000
                           San Antonio, TX 78269-6000
                           Attention: Legal Department
                           Telecopy: (210)592-2202

                           If to the Entities:

                           Shamrock Logistics GP, LLC
                           P.O. Box 696000
                           San Antonio, TX 78269-6000
                           Attention: President
                           Telecopy: (210)592-2202

Notice given by personal delivery or mail shall be effective upon actual
receipt. Notice given by 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. Any party may change any address to which
Notice is to be given to it by giving Notice as provided above of such change of
address.

                  16. 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 as may be required for Diamond
to provide the Services hereunder and to perform such other additional acts as
may be necessary or appropriate to effectuate, carry out, and perform all of the
terms, provisions, and conditions of this Agreement.



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                  17. Designated Contact Person.

                  Without limiting the obligations of the parties hereto with
respect to the delivery of notices, requests or consents pursuant to sections 14
and 15, Diamond hereby designates ___________________ (phone no. (___________)
as a person with whom representatives of the Entities may communicate regarding
any Services to be performed hereunder. The Entities hereby designate
_____________________ (phone no. (_______________) as its designated person with
whom Diamond may communicate regarding any problems or other matters that
Diamond may have in providing any Service hereunder by itself or any third party
provider.

                  18. Acknowledgment Regarding Certain Provisions.

                  EACH OF THE PARTIES HERETO SPECIFICALLY ACKNOWLEDGES AND
AGREES (a) THAT IT HAS A DUTY TO READ THIS AGREEMENT AND THAT IT IS CHARGED WITH
NOTICE AND KNOWLEDGE OF THE TERMS HEREOF, (b) THAT IT HAS IN FACT READ THIS
AGREEMENT AND IS FULLY INFORMED AND HAS FULL NOTICE AND KNOWLEDGE OF THE TERMS,
CONDITIONS AND EFFECTS OF THIS AGREEMENT, (c) THAT IT HAS BEEN REPRESENTED BY
LEGAL COUNSEL OF ITS CHOICE THROUGHOUT THE NEGOTIATIONS PRECEDING THE EXECUTION
OF THIS AGREEMENT AND HAS RECEIVED THE COUNSEL IN CONNECTION WITH ENTERING INTO
THIS AGREEMENT, AND (d) THAT IT RECOGNIZES THAT CERTAIN OF THE TERMS OF THIS
AGREEMENT PROVIDE FOR THE ASSUMPTION BY ONE PARTY OF, AND/OR RELEASE OF THE
OTHER PARTY FROM, CERTAIN LIABILITIES ATTRIBUTABLE TO THE MATTERS COVERED BY
THIS AGREEMENT THAT SUCH PARTY WOULD OTHERWISE BE RESPONSIBLE FOR UNDER THE LAW.
EACH PARTY HERETO FURTHER AGREES AND COVENANTS THAT IT WILL NOT CONTEST THE
VALIDITY OR ENFORCEABILITY OF ANY SUCH PROVISIONS OF THIS AGREEMENT ON THE BASIS
THAT THE PARTY HAD NO NOTICE OR KNOWLEDGE OF SUCH PROVISION OR THAT SUCH
PROVISIONS ARE NOT "CONSPICUOUS".



                                      -13-
<PAGE>   14

                  19. Definitions. The following terms shall have the indicated
meanings for the purposes of this Agreement:

                  "Affiliate" shall have the meaning attributed to such term in
         the Master Partnership Agreement; provided, however, that for the
         purposes of this Agreement neither the General Partner, the General
         Partner Partnership, the Master Partnership, the Operating Partnership,
         nor any Person controlled by the Master Partnership or the Operating
         Partnership (as the term "control" is used in the definition of
         "Affiliate" in the Master Partnership Agreement) shall be deemed to be
         an Affiliate of Diamond.

                  "Common Units" shall mean limited partnership interests that
         have been so designated under the terms of the Master Partnership
         Agreement.

                  "Master Partnership Agreement" shall mean the Second Amended
         and Restated Agreement of Limited Partnership of the Master
         Partnership, as it may be hereafter amended or restated.

                  20. No Third Party Beneficiary. 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 General Partner and the General Partner Partnership, to enforce
any provision of this Agreement or to compel any party to this Agreement to
comply with the terms of this Agreement.

                  21. Duration; Termination. This Agreement shall terminate upon
the eighth anniversary of the Effective Date (the "Initial Term"); provided that
this Agreement shall automatically continue for successive two year terms after
the Initial Term unless or until one year's advance notice is given to terminate
this Agreement is given by Diamond or the General Partner Partnership, in which
case this agreement shall terminate one year after such notice is delivered.
Notwithstanding the foregoing, the General Partner Partnership (a) may terminate
the provision of one or more Other Services or reduce the level of one or more
Other Services in accordance with the provisions of Section 2 hereof and (b)
shall have the right at any time to terminate this Agreement by giving written
notice to Diamond, and in such event this Agreement shall terminate one hundred
and eighty (180) days from the date on which such notice is given.



                                      -14-
<PAGE>   15




                  IN WITNESS WHEREOF, the parties hereto have caused this
Agreement to be signed on their behalf by their duly authorized officers on the
date first above written.


                                       DIAMOND SHAMROCK REFINING AND MARKETING
                                       COMPANY, ON BEHALF OF ITSELF AND ITS
                                       AFFILIATES LISTED ON SCHEDULE A



                                       By:
                                          --------------------------------------
                                          --------------------------------------




                                       SHAMROCK LOGISTICS, L.P.

                                            BY: RIVERWALK LOGISTICS, L.P.,
                                                its General Partner

                                                BY: SHAMROCK LOGISTICS GP, LLC,
                                                    its General Partner

                                                    By:
                                                       -------------------------
                                                    Its:
                                                        ------------------------





                                       SHAMROCK LOGISTICS OPERATIONS, L.P.

                                            BY: RIVERWALK LOGISTICS, L.P.,
                                                its General Partner

                                                BY: SHAMROCK LOGISTICS GP, LLC,
                                                    its General Partner

                                                    By:
                                                       -------------------------
                                                    Its:
                                                        ------------------------



                                      -15-
<PAGE>   16

                                       RIVERWALK LOGISTICS, LP

                                            BY: SHAMROCK LOGISTICS GP, LLC,
                                                its General Partner

                                                By:
                                                   -----------------------------
                                                Its:
                                                    ----------------------------

                                            SHAMROCK LOGISTICS GP, LLC,


                                                By:
                                                   -----------------------------
                                                Its:
                                                    ----------------------------



                                      -16-
<PAGE>   17

                                    EXHIBIT A

Diamond Shamrock Refining Company, L.P.
Sigmor Corporation
TPI Pipeline Corporation
The Shamrock Pipe Line Corporation



                                      -17-
<PAGE>   18

                                    EXHIBIT B


CORPORATE, GENERAL AND ADMINISTRATIVE SERVICES

Aviation and Travel Services
Corporate Development
Financial Accounting and Reporting
Foreign Trade Zone Reporting and Accounting
Group Accounting
Health and Safety Services
Human Resources Services
     Benefits
     Benefit Accounting
     Benefit Plans
     Retirement Plans
     401(k) Savings Plans
     Payroll Services
     Training Services
Internal Audit
Legal
     General Litigation Support
     General Corporate
     Corporate Secretary
     Tariff Maintenance
Office Services
     Mail Center
     Health Club
     Building and Office Maintenance
Purchasing/Fleet Management
Records Management
Real Estate Management
Risk and Claims Management Services
Security Services
Shareholder, Investor, Public, and Government Relations
Tax Accounting
Treasury & Banking
     Finance Services
     Cash Management
     Credit Services
Data Processing and Information Technology Services



                                      -18-
<PAGE>   19

                                    EXHIBIT C

Costs incurred in the Pipeline and Terminal Operating and Maintenance
Departments include the following:

         o        Construction

         o        Safety

         o        Engineering

         o        Right of Way

         o        Corrosion Control

         o        SCADA and Automation

         o        Control Centers

         o        Product and Crude Administration

         o        In addition to the above departments, there are direct
                  operating personnel that operating the individual pipelines
                  and terminals.

Costs incurred in the Operations and Maintenance of the Pipelines and Terminals
include the following:

o        Salary, Wages and Benefits Costs for Employees devoted to the operation
         and maintenance of the MLP assets. Including the following:

         -Gross payroll, including bonuses

         -FICA

         -Vacation pay

         -Sick pay

         -Life insurance

         -Disability insurance

         -401(k) matching contribution costs (qualified and non-qualified plans)

         -Defined benefit pension costs

         -Post retirement health and medical costs

o        Insurance Costs for the following insurance coverages:

         -General liability

         -Automobile liability

         -Comprehensive liability

         -Excess liability

         -Property

         -Directors & Officers

o        Other Costs incurred by the MLP or Employees devoted to the operation
         and maintenance of the MLP assets.



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