Document:

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                                                                    EXHIBIT 10.7

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                                OMNIBUS AGREEMENT

                                      among

                      ULTRAMAR DIAMOND SHAMROCK CORPORATION

                           SHAMROCK LOGISTICS GP, LLC

                            RIVERWALK LOGISTICS, L.P.

                                       and

                            SHAMROCK LOGISTICS, L.P.

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                                OMNIBUS AGREEMENT

         THIS OMNIBUS AGREEMENT is entered into on, and effective as of, the
Closing Date by and among Ultramar Diamond Shamrock Corporation, a Delaware
corporation ("UDS"), Shamrock Logistics GP, LLC, a Delaware limited liability
company ("Shamrock GP"), Riverwalk Logistics, L.P., a Delaware limited
partnership and general partner of the MLP ("Riverwalk") and Shamrock Logistics,
L.P., a Delaware limited partnership (the "MLP").

                                    RECITAL:

         UDS, the MLP, Shamrock GP in its capacity as the general partner of
Riverwalk, and Riverwalk in its capacity as the general partner of each of the
MLP and Shamrock Logistics Operations L.P., a Delaware limited partnership (the
"OLP"), desire by their execution of this Agreement to evidence their
understanding, (i) as more fully set forth in Article II of this Agreement, with
respect to (a) those business opportunities that UDS will not pursue unless the
MLP 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 accepted or declined; and (ii) as more fully set forth in Article III of
this Agreement, with respect to the indemnification obligations of UDS in favor
of relating to certain environmental liabilities.

         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
herein 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 have the meaning attributed to such term in
         the MLP Agreement.

                  "Agreement" means this Omnibus Agreement, as amended,
         modified, or supplemented from time to time in accordance with the
         terms hereof.

                  "Authority" shall mean any governmental, regulatory or
         administrative body, agency, subdivision or authority, any court or
         judicial authority, any public, private or industry regulatory
         authority, whether in the United States of America or any foreign
         country and whether national, Federal, state or local or otherwise, or
         any Person lawfully empowered by any of the foregoing to enforce or
         seek compliance with any Regulation.

                  "Change of Control" shall have the meaning attributed to such
         term in Section 2.4.

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                  "Claim" means any claim, lawsuit, demand, suit, inquiry made,
         hearing, investigation, notice of a violation, litigation, proceeding,
         arbitration, or other dispute, whether civil, criminal, administrative
         or otherwise.

                  "Closing Date" means the date of the closing of the initial
         public offering of common units representing limited partner interests
         in the MLP.

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

                  "Contaminant" means any substance regulated under any
         Environmental Law, or any substance defined as or included in the
         statutory or regulatory definitions of hazardous substances, hazardous
         wastes, hazardous materials, or "toxic substances" under any
         Environmental Law.

                  "Contract" means any agreement, contract, commitment, or other
         binding arrangement or understanding, whether written or oral.

                  "Environmental Law" means any and all laws, statutes,
         judgments, ordinances, rules, regulations, orders, determinations,
         interpretations, or guidance of any Governmental Authority pertaining
         to health or the environment in effect in any and all jurisdictions in
         which any UDS Entity or Partnership Entity or any of their respective
         Affiliates is conducting or at any time has conducted business, or
         where any property of any UDS Entity or Partnership Entity or any of
         their respective Affiliates, whether leased or owned, is located, or
         where any hazardous substances generated or disposed of by any UDS
         Entity or Partnership Entity or any of their respective Affiliates are
         located.

                  "Environmental Liabilities and Costs" means all Losses from
         any Claim by any Person whether based on Contract, tort, implied or
         express warranty, strict liability, criminal or civil statute,
         including under any Remedial Action, Environmental Law, Environmental
         Permit, Environmental Lien, Order or agreement with any Authority,
         arising from environmental, health or safety conditions, or the release
         of a Contaminant into the environment.

                  "Environmental Lien" means any Lien in favor of any Authority
         for Environmental Liabilities and Costs.

                  "Environmental Permit" shall mean any Permit, license,
         approval, consent or other authorization required by or pursuant to any
         applicable Environmental Law.

                  "Exchange Act" means the Securities Exchange Act of 1934, as
         amended.

                  "Formation Transactions" means (i) the contributions to the
         OLP of certain crude oil pipeline and storage assets and refined
         product pipeline and terminalling assets pursuant to that certain
         Conveyance, Assignment and Bill of Sale Agreements dated effective as
         of July 1, 2000, by and among the OLP and certain subsidiaries of UDS
         and

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         (ii) the transfers of certain crude oil pipeline and storage assets and
         refined product pipeline and terminalling assets and certain ownership
         interests in Skelly-Belvieu Pipeline Company, L.L.C. to the OLP by
         virtue of the mergers of certain subsidiaries of UDS with and into the
         OLP effective as of July 1, 2000.

                   "Governmental Authority" shall mean (a) the United States of
         America, (b) any state, county, municipality, or other governmental
         subdivision within the United States of America, and (c) any court or
         any governmental department, commission, board, bureau, agency, or
         other instrumentality of the United States of America or of any state,
         county, municipality, water rights, taxing, or zoning authority, or
         other governmental subdivision within the United States of America.

                  "Indemnified Party" shall have the meaning assigned to such
         term in Section 3.2(a).

                  "Indemnifying Party" shall have the meaning assigned to such
         term in Section 3.2(a).

                  "Losses" means all liabilities, losses, costs, damages
         (including punitive, consequential and treble damages), penalties or
         expenses (including, without limitation, reasonable attorneys' fees and
         expenses and costs of investigation and litigation), and also including
         any expenditures or expenses incurred to cover, remedy or rectify any
         such Losses.

                  "MLP" means Shamrock Logistics, L.P., a Delaware limited
         partnership, and any successors thereto.

                  "MLP Agreement" means the Second Amended and Restated
         Agreement of Limited Partnership of the MLP, dated as of the Closing
         Date, as such agreement is in effect on the Closing Date, to which
         reference is hereby made for all purposes of this Agreement. No
         amendment or modification to the MLP Agreement subsequent to the
         Closing Date shall be given effect for the purposes of this Agreement
         unless consented to by each of the parties to this Agreement.

                  "OLP" means Shamrock Logistics Operations, L.P., a Delaware
         limited partnership, and any successors thereto.

                  "Partnership Entities" means Shamrock GP, Riverwalk, the MLP
         and the OLP.

                   "Person" means an individual, partnership, corporation,
         limited liability company, trust, incorporated or unincorporated
         association, joint venture, joint stock company, Governmental Authority
         or other legal entity of any kind.

                  "Permits" means any licenses, permits, registrations,
         variances, interim permits, permit applications, certificates,
         approvals or other authorizations under any Regulation applicable to
         any UDS Entity or Partnership Entity.

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                  "Order" means any decree, order, injunction, rule, judgment,
         consent of or by an Authority.

                  "Regulation" means any law, statute, regulation, ruling, rule,
         Order or Permit, of, administered or enforced by or on behalf of any
         Authority, as may be amended from time to time.

                  "Remedial Action" means all actions required to (a) clean up,
         remove, treat or in any other way address Contaminants in the indoor or
         outdoor environment; (b) prevent the release or threat of release or
         minimize the further release of Contaminants so they do not migrate or
         endanger or threaten to endanger public health or welfare or the indoor
         or outdoor environment; or (c) perform pre-remedial studies and
         investigations and post-remedial monitoring and care.

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

                  "Riverwalk" means Riverwalk Logistics, L.P., a Delaware
         limited partnership and general partner of the MLP.

                  "Shamrock GP" means Shamrock GP, LLC, a Delaware limited
         liability company and general partner of Riverwalk.

                  "UDS" means Ultramar Diamond Shamrock Corporation.

                  "UDS Entities" means UDS and any of its Affiliates, other than
         the Partnership Entities.

                  "Voting Stock" means securities or membership interests of any
         class or series of either UDS, Shamrock GP or Riverwalk entitling the
         holders thereof to vote on a regular basis in the election of members
         of the board of directors, board of managers or other governing body of
         such entity.

                                  ARTICLE II.
                             BUSINESS OPPORTUNITIES

         2.1 RESTRICTED BUSINESSES. Subject to the terms of the MLP Agreement,
for as long as (i) Shamrock GP (or any Affiliate of UDS) is the general partner
of Riverwalk and (ii) Riverwalk (or any Affiliate of UDS) is the general partner
of the MLP or the OLP, each of the UDS Entities are prohibited from engaging in,
whether by acquisition or otherwise, the business of transporting crude oil or
refined petroleum products (including petrochemicals) or operating crude oil
storage or refined petroleum products terminalling assets in the United States
(a "Restricted Business").

         2.2 PERMITTED EXCEPTIONS. Notwithstanding any provision of Section 2.1,
an UDS Entity may pursue an opportunity to purchase or invest in, and may
ultimately purchase, own and/or operate, a Restricted Business under any of the
following circumstances:

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                  (a)      Any business retained by a UDS Entity at the Closing;

                  (b)      Any further development of the Diamond-Koch Joint
                           Venture petrochemicals business;

                  (c)      Any business with a fair market value of less than
                           $10 million;

                  (d)      Any business acquired by a UDS Entity that
                           constitutes less than 50% of the fair market value of
                           a larger acquisition by such UDS Entity; provided the
                           MLP has been offered and declined (with the
                           concurrence of the Conflicts Committee) the
                           opportunity to purchase such business in accordance
                           with the procedures set forth in Section 2.3;

                  (e)      The Wichita Falls crude oil pipeline, the Nuevo
                           Laredo refined product pipeline and the Ringold crude
                           oil storage facility should the MLP decline to
                           exercise its option to purchase them pursuant to the
                           [Option Agreement(s) dated effective as of July 1,
                           2000 among the UDS Entities and the MLP]; or

                  (f)      Any logistics assets newly constructed by a UDS
                           Entity that the MLP has not offered to purchase
                           within one year of construction at fair market value,
                           not to exceed 105% of the cost to such UDS Entity.

         2.3 PROCEDURES.

                  (a) In the event that an UDS Entity becomes aware of an
opportunity to purchase a Restricted Business, then, as soon as practicable,
such UDS Entity shall notify Shamrock GP of such opportunity and deliver to
Shamrock GP all information prepared by or on behalf of such UDS Entity relating
to such potential purchase. As soon as practicable but in any event within 30
days after receipt of such notification and information, Shamrock GP, on behalf
of the Partnership, shall notify the UDS Entity that either (i) Shamrock GP, on
behalf of the Partnership, has elected, with the approval of the Conflicts
Committee, not to cause the MLP to pursue the opportunity to acquire such
Restricted Business, or (ii) Shamrock GP, on behalf of the Partnership, has
elected to cause the MLP to pursue the opportunity to acquire such Restricted
Business. If, at any time, Shamrock GP or its Affiliates abandons such
opportunity (as evidenced in writing by Shamrock GP or such Affiliates following
the request of the UDS entity), the UDS Entity may pursue such opportunity. Any
Restricted Business which is permitted to be purchased by an UDS Entity must be
so purchased (i) within 12 months of the time the UDS Entity becomes able to
pursue such acquisition in accordance with the provisions of this Section 2.3
and (ii) on terms not materially more favorable to the UDS Entity than were
offered to the Partnership. If either of these conditions are not satisfied, the
opportunity must be reoffered to the Partnership.

                  (b) In the event that an UDS Entity acquires a Restricted
Business as part of a larger transaction in accordance with the provisions of
Section 2.2(d), then, within 30 days of the consummation of such purchase, such
UDS Entity shall notify Shamrock GP of such purchase and offer the MLP the
opportunity to purchase the Restricted Business constituting a portion of

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such purchase and deliver to Shamrock GP all information prepared by or on
behalf of or in the possession of such UDS Entity relating to the Restricted
Business. As soon as practicable but in any event within 30 days after receipt
of such notification, Shamrock GP shall notify the UDS Entity that either (i)
Shamrock GP, on behalf of the Partnership, has elected, with the approval of the
Conflicts Committee, not to cause the MLP to purchase such Restricted Business,
in which event the UDS Entity shall be free to continue to engage in such
Restricted Business, or (ii) Shamrock GP, on behalf of the Partnership, has
elected to cause the MLP to purchase such Restricted Business, in which event
the following procedures shall be followed:

                           (i) The UDS Entity shall submit a good faith offer to
         Shamrock GP to sell the Restricted Business (the "Offer") to any member
         of the Partnership Group designated by Shamrock GP on the terms and for
         the consideration stated in the Offer.

                           (ii) The UDS Entity and Shamrock GP shall negotiate
         in good faith, for 60 days after receipt of such Offer by Shamrock GP,
         the terms on which the Restricted Business will be sold to the MLP. The
         UDS Entity shall provide all information concerning the business,
         operations and finances of such Restricted Business as may be
         reasonably requested by Shamrock GP.

                                    (A) If the UDS Entity and Shamrock GP agree
                  on such terms within 60 days after receipt by Shamrock GP of
                  the Offer, the MLP shall purchase the Restricted Business on
                  such terms as soon as commercially practicable after such
                  agreement has been reached.

                                    (B) If the UDS Entity and Shamrock GP are
                  unable to agree on the terms of a sale during such 60-day
                  period, the UDS Entity shall attempt to sell the Restricted
                  Business to a Person that is not an Affiliate of the UDS
                  Entity (a "NonAffiliate Purchaser") within nine months of the
                  termination of such 60-day period. Any such sale to a
                  NonAffiliate Purchaser must be for a purchase price, as
                  determined by the board of directors of UDS, not less than 95%
                  of the purchase price last offered by the MLP.

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

                                    (A) If Shamrock GP, with the concurrence of
                  the Conflicts Committee, elects not to cause the MLP to pursue
                  the Second Offer, the UDS Entity shall be free to continue to
                  engage in such Restricted Business.

                                    (B) If Shamrock GP shall elect to cause the
                  MLP to purchase such Restricted Business, then Shamrock GP and
                  the UDS Entity shall negotiate the terms of such purchase for
                  60 days. If the UDS Entity and Shamrock GP agree on such terms
                  within 60 days after receipt by Shamrock GP of the Second

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                  Offer, the MLP shall purchase the Restricted Business on such
                  terms as soon as commercially practicable after such agreement
                  has been reached.

                                    (C) If during such 60-day period, no
                  agreement has been reached between the UDS Entity and Shamrock
                  GP or a member of the Partnership Group, the UDS Entity and
                  Shamrock GP 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 UDS Entity and Shamrock GP its opinion of such
                  value. The UDS Entity and Shamrock GP shall share equally the
                  fees and expenses of such investment banking firm. Upon
                  receipt of such opinion, Shamrock GP will have the option,
                  subject to the approval of the Conflicts Committee, to (A)
                  cause the MLP 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 UDS 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
UDS upon or at any time after a "Change of Control" of UDS or each of Shamrock
GP or Riverwalk by written notice to the MLP. A Change of Control of UDS or each
of Shamrock GP or Riverwalk 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 UDS or Shamrock GP to any Person or its
Affiliates, unless immediately following such sale, lease, exchange or other
transfer such assets are owned, directly or indirectly, by the UDS Entities or
Shamrock GP; (ii) the consolidation or merger of UDS or Shamrock GP with or into
another Person pursuant to a transaction in which the outstanding Voting Stock
of UDS or Shamrock GP is changed into or exchanged for cash, securities or other
property, other than any such transaction where (a) the outstanding Voting Stock
of UDS or Shamrock GP is changed into or exchanged for Voting Stock of the
surviving corporation or its parent and (b) the holders of the Voting Stock of
UDS or Shamrock GP 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; or (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
UDS or Shamrock GP then outstanding, other than in a merger or consolidation
which would not constitute a Change of Control under clause (ii) above.

         2.5 SCOPE OF RESTRICTED BUSINESS PROHIBITION. Except as provided in
this Article II and the Partnership Agreement, each UDS Entity shall be free to
engage in any business activity whatsoever, including those that may be in
direct competition with any Partnership Entity.

         2.6 ENFORCEMENT. The UDS Entities agree and acknowledge that the
Partnership Group does not have an adequate remedy at law for the breach by the
UDS Entities of

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the covenants and agreements set forth in this Article II, and that any breach
by the UDS Entities of the covenants and agreements set forth in Article II
would result in irreparable injury to the Partnership Group. The UDS Entities
further agree and acknowledge that any member of the Partnership Group may, in
addition to the other remedies which may be available to the Partnership Group
hereunder or under applicable law, file a suit in equity to enjoin the UDS
Entities from such breach, and consent to the issuance of injunctive relief
hereunder.

                                  ARTICLE III.
                                 INDEMNIFICATION

         3.1 Indemnification of Partnership Entities by UDS(a) . In addition to
its indemnification obligations under that certain (i) Indemnification
Agreements entered into in connection with the mergers of certain subsidiaries
of UDS with and into the OLP effective as of July 1, 2000, and (ii) Conveyance,
Assignment and Bill of Sale Agreements dated effective as of July 1, 2000, by
and among the OLP and certain subsidiaries of UDS, UDS, on behalf of each of the
respective UDS Entities, shall indemnify, defend and hold harmless the
Partnership Entities from and against any and all Losses that are caused by,
arise out of or are attributable to Environmental Liabilities and Costs related
to the assets transferred by the UDS Entities to the MLP in connection with the
Formation Transactions that arose prior to Closing and which are discovered by
the MLP within 10 years of the Closing (excluding Environmental Liabilities and
Costs resulting from a change in law after closing).

         3.2 INDEMNIFICATION PROCEDURES.

                  (a) As used in this Section 3.2, the term "Indemnifying Party"
refers to UDS in the case of any indemnification obligation arising under
Section 3.1, and the term "Indemnified Party" refers to the Partnership
Entities, as applicable, in the case of any indemnification obligation arising
under Section 3.1.

                  (b) If any action, suit or proceeding shall be brought against
an Indemnified Party, or if the Indemnified Party should otherwise become aware
of facts giving rise to a claim for indemnification pursuant to Section 3.1 the
Indemnified Party shall promptly notify the Indemnifying Party in writing
specifying the nature of and specific basis for such claim.

                  (c) The Indemnifying Party shall have the right to control all
aspects of the defense of (and any counterclaims with respect to) any claims
brought against the Indemnified Party that are covered by the indemnification
set forth in Section 3.1, including, without limitation, the selection of
counsel, determination of whether to appeal any decision of any court and the
settling of any such matter or any issues relating thereto; provided, however,
that no such settlement shall be entered into without the consent of the
Indemnified Party unless it includes a full release of the Indemnified Party
from such matter or issues, as the case may be.

                  (d) The Indemnified Party agree, at its own cost and expense,
to cooperate fully with the Indemnifying Party with respect to all aspects of
the defense of any claims covered by the indemnification set forth in Section
3.1, including, without limitation, the prompt furnishing to the Indemnifying
Party of any correspondence or other notice relating thereto that the
Indemnified Party may receive, permitting the name(s) of the Indemnified Party
to be utilized in connection with such defense, the making available to the
Indemnifying Party of any files,

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records or other information of the Indemnified Party that the Indemnifying
Party considers relevant to such defense and the making available to the
Indemnifying Party of any employees of the Indemnified Party; provided, however,
that in connection therewith the Indemnifying Party agrees to use reasonable
efforts to minimize the impact thereof on the operations of such Indemnified
Party. In no event shall the obligation of the Indemnified Party to cooperate
with the Indemnifying Party as set forth in the immediately preceding sentence
be construed as imposing upon the Indemnified Party an obligation to hire and
pay for counsel in connection with the defense of any claims covered by the
indemnification set forth in this Article III; provided, however, that the
Indemnified Party may, at their own option, cost and expense, hire and pay for
counsel in connection with any such defense. The Indemnifying Party agrees to
keep any such counsel hired by the Indemnified Party reasonably informed as to
the status of any such defense, but the Indemnifying Party shall have the right
to retain sole control over such defense.

                  (e) In determining the amount of any loss, liability or
expense for which any Indemnified Party is entitled to indemnification under
this Article III, the gross amount thereof will be reduced by any insurance
proceeds realized or to be realized by such Indemnified Party, and such
correlative insurance benefit shall be net of any insurance premium that becomes
due as a result of such claim.

                                  ARTICLE IV.
                                  MISCELLANEOUS

         4.1 CHOICE OF LAW; SUBMISSION TO JURISDICTION. This Agreement shall be
subject to and governed by the laws of the State of Delaware, excluding any
conflicts-of-law rule or principle that might refer the construction or
interpretation of this Agreement to the laws of another state.

         4.2 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
5.2.

         4.3 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.

         4.4 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

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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.

         4.5 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 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 Shamrock GP, 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.

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

         4.7 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.

         4.8 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.

         4.9 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, unless the context otherwise
requires.

         4.10 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.

         4.11 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.

         4.12 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.

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         4.13 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, 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 Closing Date.

                                             ULTRAMAR DIAMOND SHAMROCK
                                             CORPORATION

                                             By:
                                                --------------------------------
                                             Name:
                                                  ------------------------------
                                             Title:
                                                   -----------------------------

                                             Address for Notice:
                                                                ----------------

                                             Telecopy Number:
                                                             -------------------

                                             SHAMROCK LOGISTICS GP, LLC

                                             By:
                                                --------------------------------
                                             Name:
                                                  ------------------------------
                                             Title:
                                                   -----------------------------

                                             Address for Notice:
                                                                ----------------

                                             Telecopy Number:
                                                             -------------------

<PAGE>   14

                                             RIVERWALK LOGISTICS, L.P.

                                             By: Shamrock Logistics GP, LLC
                                                 its general partner

                                             By:
                                                -------------------------------
                                             Name:
                                                  -----------------------------
                                             Title:
                                                   ----------------------------

                                             Address for Notice:
                                                                ---------------

                                             Telecopy Number:
                                                             ------------------

                                             SHAMROCK LOGISTICS, L.P.

                                             By: Riverwalk Logistics, L.P.
                                                 its general partner

                                             By: Shamrock Logistics GP, LLC
                                                 Its general partner

                                             By:
                                                -------------------------------
                                             Name:
                                                  -----------------------------
                                             Title:
                                                   ----------------------------

                                             Address for Notice:
                                                                ---------------

                                             Telecopy Number:
                                                             ------------------<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-
<PAGE>   3

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-
<PAGE>   6

         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.

                                      -8-
<PAGE>   9

                  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-
<PAGE>   10

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

                                      -10-
<PAGE>   11

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

                                      -11-
<PAGE>   12

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.

                                      -12-
<PAGE>   13

                  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.

                                      -19-

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