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                                                                     EXHIBIT 4.3
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                            VALERO ENERGY CORPORATION


                               GUARANTEE AGREEMENT


                                   VEC TRUST I




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                            Dated as of June 28, 2000

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                                TABLE OF CONTENTS
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                                                     ARTICLE I
                                                    DEFINITIONS


SECTION 1.01      Definitions.....................................................................................1

                                                     ARTICLE II
                                                TRUST INDENTURE ACT


SECTION 2.01      Trust Indenture Act; Application................................................................5
SECTION 2.02      Lists of Holders of Preferred Securities........................................................5
SECTION 2.03      Reports by the Guarantee Trustee................................................................6
SECTION 2.04      Periodic Reports to the Guarantee Trustee.......................................................6
SECTION 2.05      Evidence of Compliance with Conditions Precedent................................................6
SECTION 2.06      Events of Default; Waiver.......................................................................7
SECTION 2.07      Disclosure of Information.......................................................................7
SECTION 2.08      Conflicting Interest............................................................................7

                                                     ARTICLE III
                                 POWERS, DUTIES AND RIGHTS OF THE GUARANTEE TRUSTEE


SECTION 3.01      Powers and Duties of the Guarantee Trustee......................................................7
SECTION 3.02      Certain Rights and Duties of the Guarantee Trustee..............................................8
SECTION 3.03      Not Responsible for Recitals or Issuance of Guarantee..........................................10
SECTION 3.04      The Guarantee Trustee May Own Preferred Securities.............................................11
SECTION 3.05      Moneys Received by the Guarantee Trustee to Be Held in Trust Without Interest..................11
SECTION 3.06      Compensation and Expenses of Guarantee Trustee.................................................11

                                                     ARTICLE IV
                                                 GUARANTEE TRUSTEE


SECTION 4.01      Qualifications.................................................................................12
SECTION 4.02      Appointment, Removal and Resignation of the Guarantee Trustee..................................12

                                                      ARTICLE V
                                                      GUARANTEE


SECTION 5.01      Guarantee......................................................................................13
SECTION 5.02      Waiver of Notice...............................................................................13
SECTION 5.03      Obligations Not Affected.......................................................................13
SECTION 5.04      Enforcement of Guarantee.......................................................................14
SECTION 5.05      Guarantee of Payment...........................................................................15
SECTION 5.06      Subrogation....................................................................................15
SECTION 5.07      Independent Obligations........................................................................15
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                                                     ARTICLE VI
                                     LIMITATION OF TRANSACTIONS; SUBORDINATION


SECTION 6.01      Limitation of Transactions.....................................................................16
SECTION 6.02      Subordination..................................................................................16

                                                     ARTICLE VII
                                                    TERMINATION


SECTION 7.01      Termination....................................................................................17

                                                    ARTICLE VIII
                                      LIMITATION OF LIABILITY; INDEMNIFICATION


SECTION 8.01      Exculpation....................................................................................17
SECTION 8.02      Indemnification................................................................................17
SECTION 8.03      Survive Termination............................................................................18

                                                     ARTICLE IX
                                                   MISCELLANEOUS


SECTION 9.01      Successors and Assigns.........................................................................18
SECTION 9.02      Amendments.....................................................................................18
SECTION 9.03      Notices........................................................................................18
SECTION 9.04      Genders........................................................................................19
SECTION 9.05      Benefit........................................................................................19
SECTION 9.06      Governing Law..................................................................................20
SECTION 9.07      Counterparts...................................................................................20
SECTION 9.08      Exercise of Overallotment Option...............................................................20
SECTION 9.09      Limited Liability..............................................................................20
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                               GUARANTEE AGREEMENT

         This GUARANTEE AGREEMENT, dated as of June 28, 2000, is executed and
delivered by Valero Energy Corporation, a Delaware corporation (the
"Guarantor"), and The Bank of New York, a national banking association, as the
initial Guarantee Trustee (as defined herein) for the benefit of the Holders (as
defined herein) from time to time of the Preferred Securities (as defined
herein) of VEC Trust I, a Delaware statutory business trust (the "Issuer").

         WHEREAS, pursuant to an Amended and Restated Declaration of Trust (the
"Declaration"), dated as of June 28, 2000 among the trustees of the Issuer named
therein, Valero Energy Corporation, as Sponsor, and the Holders from time to
time of preferred undivided beneficial interests in the assets of the Issuer,
the Issuer may issue up to $172,500,000 aggregate liquidation amount of its 7
3/4% Trust Preferred Securities (the "Preferred Securities") representing
preferred undivided beneficial interests in the assets of the Issuer and having
the terms set forth in the Declaration, of which $150,000,000 liquidation amount
of Preferred Securities is being issued as of the date hereof. Up to the
remaining $22,500,000 liquidation amount of Preferred Securities may be issued
by the Issuer if and to the extent that the over-allotment option granted by the
Guarantor and the Issuer pursuant to the Underwriting Agreement (as defined in
the Declaration) is exercised by the Underwriters named in the Underwriting
Agreement; and

         WHEREAS, as incentive for the Holders to purchase Preferred Securities,
the Guarantor desires to irrevocably and unconditionally agree, to the extent
set forth herein, to pay to the Holders the Guarantee Payments (as defined
herein) and to make certain other payments on the terms and conditions set forth
herein;

         NOW, THEREFORE, in consideration of the purchase by the initial
purchasers thereof of Preferred Securities, which purchase the Guarantor hereby
agrees shall benefit the Guarantor, the Guarantor executes and delivers this
Guarantee Agreement for the benefit of the Holders from time to time.


                                    ARTICLE I
                                   DEFINITIONS

     SECTION 1.01 Definitions.

         (a) Capitalized terms used in this Guarantee Agreement but not defined
in the preamble or recitals above have the respective meanings assigned to them
in this Section 1.01.

         (b) A term defined anywhere in this Guarantee Agreement has the same
meaning throughout.


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         (c) All references to "the Guarantee Agreement" or "this Guarantee
Agreement" are to this Guarantee Agreement as modified, supplemented or amended
from time to time.

         (d) All references in this Guarantee Agreement to Articles and Sections
are to Articles and Sections of this Guarantee Agreement unless otherwise
specified.

         (e) A term defined in the Trust Indenture Act has the same meaning when
used in this Guarantee Agreement unless otherwise defined in this Guarantee
Agreement or unless the context otherwise requires.

         (f) A reference to the singular includes the plural and vice versa.

         "Additional Amounts" has the meaning set forth in the Indenture.

         "Affiliate" of any specified Person means any other Person directly or
indirectly controlling or controlled by, or under direct or indirect common
control with, such specified Person. For purposes of this definition, "control"
of a Person shall mean the power to direct the management and policies of such
Person, directly or indirectly, whether through the ownership of voting
securities, by contract or otherwise, and the terms "controlling" and
"controlled" shall have meanings correlative to the foregoing.

         "Business Day" has the meaning set forth in the Indenture.

         "Commission" means the Securities and Exchange Commission.

         "Common Securities" means the securities representing common undivided
beneficial interests in the assets of the Issuer and having the terms set forth
in Article VII of the Declaration.

         "Common Stock" means the common stock, $.01 par value per share, of the
Guarantor, including associated preferred share purchase rights.

         "Declaration" has the meaning set forth in the recitals above.

         "Distributions" means the periodic distributions and other payments
payable to Holders in accordance with the terms of the Preferred Securities set
forth in Article VII of to the Declaration.

         "Dollar" has the meaning set forth in the Indenture.

         "Event of Default" means a default by the Guarantor on any of its
payment or other obligations under this Guarantee Agreement; provided, however,
that, except with respect to a default in payment of any Guarantee Payment, any
such default shall constitute an Event of Default

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only if the Guarantor shall have received notice of such default and shall not
have cured such default within 60 days after receipt of such notice.

         "Extension Period" has the meaning set forth in Section 2.8 of the
Supplemental Indenture.

         "Guarantee Payments" means the following payments or distributions,
without duplication, with respect to the Preferred Securities, to the extent not
paid or made by or on behalf of the Issuer: (i) any accumulated and unpaid
Distributions, any Additional Amounts payable with respect to the Preferred
Securities in accordance with the terms thereof and the Redemption Price,
including all accumulated and unpaid Distributions and Additional Amounts to the
date of redemption, with respect to the Preferred Securities called for
redemption by the Issuer but only if and to the extent that in each case the
Guarantor has made a payment to the Property Trustee of principal of, any
premium or interest on or any Additional Amounts with respect to the Notes and
(ii) upon a voluntary or involuntary dissolution, winding-up or termination of
the Issuer (other than in connection with the distribution of Notes to Holders
in exchange for Preferred Securities or the redemption of the Preferred
Securities in full upon the maturity or redemption of the Notes as provided in
the Declaration), the lesser of (a) the aggregate of the liquidation amount and
all accumulated and unpaid Distributions and Additional Amounts on the Preferred
Securities to the date of payment, to the extent the Issuer has funds on hand
legally available therefor, and (b) the amount of assets of the Issuer remaining
available for distribution to Holders in liquidation of the Issuer as required
by applicable law.

         "Guarantee Trustee" means The Bank of New York, a New York banking
corporation, until a Successor Guarantee Trustee has been appointed and has
accepted such appointment pursuant to the terms of this Guarantee Agreement, and
thereafter means each such Successor Guarantee Trustee.

         "Holder" means any holder, as registered on the books and records of
the Issuer, of any Preferred Securities; provided, however, that in determining
whether the holders of the requisite percentage of Preferred Securities have
given any request, notice, consent or waiver hereunder, "Holder" shall not
include the Guarantor or any Affiliate of the Guarantor.

         "Indemnified Person" means the Guarantee Trustee, any Affiliate of the
Guarantee Trustee, and any officers, directors, shareholders, members, partners,
employees, representatives or agents of the Guarantee Trustee.

         "Indenture" means the Indenture dated as of December 12, 1997 between
the Guarantor and The Bank of New York, as trustee, as supplemented by the First
Supplemental Indenture thereto dated as of June 28, 2000 (the "Supplemental
Indenture"), pursuant to which the Notes are to be issued to the Property
Trustee.


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         "Majority of Outstanding Preferred Securities" means Holder(s) of
outstanding Preferred Securities, voting together as a single class, who are the
record owners of Preferred Securities representing more than 50% of the
outstanding Preferred Securities.

         "Notes" means the series of unsecured senior notes issued to the
Property Trustee by the Guarantor under the Indenture and entitled the "7 3/4%
Senior Deferrable Notes due 2005."

         "Officers' Certificate" means, with respect to any Person, a
certificate signed by the Chairman of the Board, the President, any Vice
Chairman of the Board, any Vice President, the Chief Financial Officer, the
Treasurer, any Assistant Treasurer, the Controller, the Secretary or any
Assistant Secretary of such Person, and delivered to the Guarantee Trustee. One
of the officers signing an Officers' Certificate given pursuant to Section 2.04
shall be the principal executive, financial or accounting officer of the
Guarantor. Any Officers' Certificate delivered with respect to compliance with a
condition or covenant provided for in this Guarantee Agreement shall include:

         (i) a statement that the person making such certificate has read such
     covenant or condition;

         (ii) a brief statement as to the nature and scope of the examination
     or investigation upon which the statements or opinions contained in such
     certificate are based;

         (iii) a statement that, in the opinion of such person, he has made
     such examination or investigation as is necessary to enable him to express
     an informed opinion as to whether or not such covenant or condition has
     been complied with; and

         (iv) a statement as to whether or not, in the opinion of such person,
     such condition or covenant has been complied with.

         "Person" means any individual, corporation, partnership, limited
liability company, joint venture, incorporated or unincorporated association,
joint stock company, trust, unincorporated organization or government or other
agency or political subdivision thereof or other entity of any kind.

         "Preferred Securities" has the meaning set forth in the recitals above.

         "Property Trustee" means the Person acting as Property Trustee under
the Declaration.

         "Redemption Price" means the amount payable on redemption of the
Preferred Securities in accordance with the terms of the Preferred Securities.

         "Responsible Officer" means, when used with respect to the Guarantee
Trustee, any officer within the corporate trust department of the Guarantee
Trustee, including any vice president,


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assistant vice president, assistant secretary, assistant treasurer, trust
officer or any other officer of the Guarantee Trustee who customarily performs
functions similar to those performed by the Persons who at the time shall be
such officers, respectively, or to whom any corporate trust matter is referred
because of such Person's knowledge of and familiarity with the particular
subject and, in either case, who shall have direct responsibility for the
administration of this Guarantee Agreement.

         "Successor Guarantee Trustee" means a successor Guarantee Trustee
possessing the qualifications to act as a Guarantee Trustee under Section 4.01.

         "Supplemental Indenture" has the meaning specified in the definition of
Indenture.

         "Trust Enforcement Event" has the meaning specified in the Declaration.

         "Trust Indenture Act" means the Trust Indenture Act of 1939, as
amended.


                                   ARTICLE II
                               TRUST INDENTURE ACT

     SECTION 2.01 Trust Indenture Act; Application.

         (a) This Guarantee Agreement is subject to the provisions of the Trust
Indenture Act that are required to be part of this Guarantee Agreement and
shall, to the extent applicable, be governed by such provisions.

         (b) If and to the extent that any provision of this Guarantee Agreement
limits, qualifies or conflicts with the duties imposed by Sections 310 to 317,
inclusive, of the Trust Indenture Act, such imposed duties shall control.

         (c) The application of the Trust Indenture Act to this Guarantee
Agreement shall not affect the nature of the Preferred Securities as equity
securities representing preferred undivided beneficial interests in the assets
of the Issuer.

     SECTION 2.02 Lists of Holders of Preferred Securities.

         (a) The Guarantor shall provide the Guarantee Trustee (unless the
Guarantee Trustee is the registrar of the Preferred Securities) (i) within 14
days after each record date for payment of Distributions, a list, in such form
as the Guarantee Trustee may reasonably require, of the names and addresses of
the Holders ("List of Holders") as of such date, and (ii) at any other time,
within 30 days of receipt by the Guarantor of a written request for a List of
Holders as of a date no more than 15 days before such List of Holders is given
to the Guarantee Trustee; provided that in each case the Guarantor shall not be
obligated to provide such List of Holders at any time that the List of Holders
does not differ from the most recent List of Holders given to the Guarantee
Trustee



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by the Guarantor. The Guarantee Trustee shall preserve, in as current a form as
is reasonably practicable, all information contained in the Lists of Holders
given to it; provided that the Guarantee Trustee may destroy any List of Holders
previously given to it on receipt of a new List of Holders.

         (b) The Guarantee Trustee shall comply with its obligations under
Section 312(b) of the Trust Indenture Act.

     SECTION 2.03 Reports by the Guarantee Trustee.

         Within 60 days after June 15th of each year, commencing June 15, 2001,
the Guarantee Trustee shall deliver to the Holders such reports as are required
by Section 313 of the Trust Indenture Act, if any, in the form, in the manner
and at the times provided by Section 313 of the Trust Indenture Act. The
Guarantee Trustee shall also comply with the other requirements of Section 313
of the Trust Indenture Act. A copy of each such report shall, at the time of
such transmission to the Holders, be filed by the Guarantee Trustee with the
Guarantor, with each stock exchange or quotation system upon which any Preferred
Securities are listed or traded (if so listed or traded) and also with the
Commission. The Guarantor agrees to notify the Guarantee Trustee when any
Preferred Securities become listed on any stock exchange or quotation system and
of any delisting thereof.

     SECTION 2.04 Periodic Reports to the Guarantee Trustee.

         The Guarantor shall provide to the Guarantee Trustee, the Commission
and the Holders, as applicable, such documents, reports and information (if any)
as required by Section 314(a)(1)-(3) of the Trust Indenture Act and the
compliance certificates required by Section 314(a)(4) and (c) of the Trust
Indenture Act, any such certificates to be provided in the form, in the manner
and at the times required by Section 314(a)(4) and (c) of the Trust Indenture
Act (provided that any certificate to be provided pursuant to Section 314(a)(4)
of the Trust Indenture Act shall be provided within 120 days of the end of each
fiscal year of the Issuer). Delivery of such reports, information and documents
to the Guarantee Trustee is for informational purposes only and the Guarantee
Trustee's receipt of such shall not constitute constructive notice of any
information contained therein, including the Guarantor's compliance with any of
its covenants hereunder (as to which the Guarantee Trustee is entitled to rely
exclusively on Officers' Certificates or on certificates provided pursuant to
this Section 2.04).

     SECTION 2.05 Evidence of Compliance with Conditions Precedent.

         The Guarantor shall provide to the Guarantee Trustee such evidence of
compliance with any conditions precedent, if any, provided for in this Guarantee
Agreement which relate to any of the matters set forth in Section 314(c) of the
Trust Indenture Act. Any certificate or opinion required to be given by an
officer pursuant to Section 314(c) may be given in the form of an Officers'
Certificate.



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     SECTION 2.06 Events of Default; Waiver.

         (a) The Holders of a Majority of Outstanding Preferred Securities may,
by vote, on behalf of the Holders, waive any past Event of Default and its
consequences. Upon such waiver, any such Event of Default shall cease to exist,
and any Event of Default arising therefrom shall be deemed to have been cured,
for every purpose of this Guarantee Agreement, but no such waiver shall extend
to any subsequent or other default or Event of Default, or impair any right
consequent thereon.

         (b) The right of any Holder to receive payment of the Guarantee
Payments in accordance with this Guarantee Agreement, or to institute suit for
the enforcement of any such payment, shall not be impaired without the consent
of each such Holder.

     SECTION 2.07 Disclosure of Information.

         The disclosure of information as to the names and addresses of the
Holders in accordance with Section 312 of the Trust Indenture Act, regardless of
the source from which such information was derived, shall not be deemed to be a
violation of any existing law, or any law hereafter enacted which does not
specifically refer to Section 312 of the Trust Indenture Act, nor shall the
Guarantee Trustee be held accountable by reason of mailing any material pursuant
to a request made under Section 312(b) of the Trust Indenture Act.

     SECTION 2.08 Conflicting Interest.

         (a) The Declaration shall be deemed to be specifically described in
this Guarantee Agreement for the purposes of clause (i) of the first proviso
contained in Section 310(b) of the Trust Indenture Act.

         (b) The Guarantee Trustee shall comply with its obligations under
Sections 310(b) and 311 of the Trust Indenture Act.


                                   ARTICLE III
               POWERS, DUTIES AND RIGHTS OF THE GUARANTEE TRUSTEE

     SECTION 3.01 Powers and Duties of the Guarantee Trustee.

         (a) This Guarantee Agreement shall be held by the Guarantee Trustee in
trust for the benefit of the Holders. The Guarantee Trustee shall not transfer
its right, title and interest in this Guarantee Agreement to any Person except a
Successor Guarantee Trustee on acceptance by such Successor Guarantee Trustee of
its appointment to act as Guarantee Trustee or to a Holder exercising his or her
rights pursuant to Section 5.04(iv). The right, title and interest of the
Guarantee Trustee to this Guarantee Agreement shall vest automatically in each
Person who may hereafter be appointed


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as Guarantee Trustee in accordance with Article IV. Such vesting and cessation
of title shall be effective whether or not conveyancing documents have been
executed and delivered.

         (b) If an Event of Default has occurred and is continuing, the
Guarantee Trustee shall enforce this Guarantee Agreement for the benefit of the
Holders.

         (c) This Guarantee Agreement and all moneys received by the Guarantee
Trustee in respect of the Guarantee Payments will not be subject to any right,
charge, security interest, lien or claim of any kind in favor of, or for the
benefit of, the Guarantee Trustee or its agents or their creditors.

         (d) The Guarantee Trustee shall, within 90 days after the occurrence of
an Event of Default actually known to a Responsible Officer of the Guarantee
Trustee, transmit by mail, first class postage prepaid, to the Holders, as their
names and addresses appear upon the List of Holders, notice of all such Events
of Default, unless such defaults shall have been cured before the giving of such
notice; provided that the Guarantee Trustee shall be protected in withholding
such notice if and so long as the board of directors, the executive committee or
a trust committee of directors and/or Responsible Officers of the Guarantee
Trustee in good faith determines that the withholding of such notice is in the
interests of the Holders. The Guarantee Trustee shall not be deemed to have
knowledge of any Event of Default except any Event of Default as to which the
Guarantee Trustee shall have received written notice or a Responsible Officer
charged with the administration of this Guarantee Agreement shall have obtained
written notice of such Event of Default.

         (e) The Guarantee Trustee shall continue to serve as a trustee until a
Successor Guarantee Trustee has been appointed and accepted that appointment in
accordance with Article IV.

     SECTION 3.02 Certain Rights and Duties of the Guarantee Trustee.

         (a) The Guarantee Trustee, before the occurrence of an Event of Default
and after the curing or waiving of all Events of Default that may have occurred,
shall undertake to perform only such duties as are specifically set forth in
this Guarantee Agreement, and no implied covenants shall be read into this
Guarantee Agreement against the Guarantee Trustee. In case an Event of Default
has occurred (that has not been cured or waived pursuant to Section 2.06), the
Guarantee Trustee shall exercise such of the rights and powers vested in it by
this Guarantee Agreement, and use the same degree of care and skill in its
exercise thereof, as a prudent person would exercise or use under the
circumstances in the conduct of his own affairs.

         (b) No provision of this Guarantee Agreement shall be construed to
relieve the Guarantee Trustee from liability for its own negligent action, its
own negligent failure to act or its own willful misconduct, except that:

         (i) prior to the occurrence of an Event of Default and after the
     curing or waiving of all such Events of Default that may have occurred:


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               (A) the duties and obligations of the Guarantee Trustee shall be
          determined solely by the express provisions of this Guarantee
          Agreement, and the Guarantee Trustee shall not be liable except for
          the performance of such duties and obligations as are specifically set
          forth in this Guarantee Agreement, and no implied covenants or
          obligations shall be read into this Guarantee Agreement against the
          Guarantee Trustee; and

               (B) in the absence of willful misconduct on the part of the
          Guarantee Trustee, the Guarantee Trustee may conclusively rely, as to
          the truth of the statements and the correctness of the opinions
          expressed therein, upon any certificates or opinions furnished to the
          Guarantee Trustee and conforming to the requirements of this Guarantee
          Agreement; provided, however, that in the case of any such
          certificates or opinions that by any provision hereof or the Trust
          Indenture Act are specifically required to be furnished to the
          Guarantee Trustee, the Guarantee Trustee shall be under a duty to
          examine the same to determine whether or not they conform to the
          requirements of this Guarantee Agreement or the Trust Indenture Act,
          as the case may be (but need not confirm or investigate the accuracy
          of mathematical calculations or other facts stated therein);

          (ii) the Guarantee Trustee shall not be liable for any error of
     judgment made in good faith by a Responsible Officer of the Guarantee
     Trustee, unless it shall be proved that the Guarantee Trustee was negligent
     in ascertaining the pertinent facts upon which such judgment was made;

          (iii) the Guarantee Trustee shall not be liable with respect to any
     action taken or omitted to be taken by it in good faith in accordance with
     the direction of the Holders of a Majority of Outstanding Preferred
     Securities relating to the time, method and place of conducting any
     proceeding for any remedy available to the Guarantee Trustee, or exercising
     any trust or power conferred upon the Guarantee Trustee under this
     Guarantee Agreement; and

          (iv) no provision of this Guarantee Agreement shall require the
     Guarantee Trustee to expend or risk its own funds or otherwise incur
     personal financial liability in the performance of any of its duties or in
     the exercise of any of its rights or powers, if it shall have reasonable
     grounds for believing that the repayment of such funds or liability is not
     reasonably assured to it under the terms of this Guarantee Agreement or
     indemnity reasonably satisfactory to it against such risk or liability is
     not reasonably assured to it.

     (c) Subject to the provisions of Section 3.02(a) and (b):

          (i) whenever in the administration of this Guarantee Agreement, the
     Guarantee Trustee shall deem it desirable that a matter be proved or
     established prior to taking, suffering or omitting any action hereunder,
     the Guarantee Trustee (unless other evidence is


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<PAGE>   13

     herein specifically prescribed) may, in the absence of willful misconduct
     on its part, request and rely upon an Officers' Certificate, which, upon
     receipt of such request, shall be promptly delivered by the Guarantor;

          (ii) the Guarantee Trustee (A) may consult with counsel (which may be
     counsel to the Guarantor or any of its Affiliates and may include any of
     its employees) selected by it in good faith and with due care and the
     advice or opinion of such counsel with respect to legal matters shall be
     full and complete authorization and protection in respect of any action
     taken, suffered or omitted by it hereunder in good faith and in reliance
     thereon and in accordance with such advice and opinion and (B) shall have
     the right at any time to seek, at the expense of the Guarantor,
     instructions concerning the administration of this Guarantee Agreement from
     any court of competent jurisdiction;

          (iii) the Guarantee Trustee may execute any of the trusts or powers
     hereunder or perform any duties hereunder either directly or by or through
     agents or attorneys, and the Guarantee Trustee shall not be responsible for
     any willful misconduct or negligence on the part of any agent or attorney
     appointed by it in good faith and with due care;

          (iv) the Guarantee Trustee shall be under no obligation to exercise
     any of the rights or powers vested in it by this Guarantee Agreement at the
     request or direction of any Holder, unless such Holder shall have offered
     to the Guarantee Trustee security and indemnity satisfactory to the
     Guarantee Trustee against the costs, expenses (including attorneys' fees
     and expenses) and liabilities that might be incurred by it in complying
     with such request or direction; provided that nothing contained in this
     clause (iv) shall relieve the Guarantee Trustee of the obligation, upon the
     occurrence of an Event of Default (which has not been cured or waived) to
     exercise such of the rights and powers vested in it by this Guarantee
     Agreement, and to use the same degree of care and skill in this exercise as
     a prudent person would exercise or use under the circumstances in the
     conduct of his own affairs; and

          (v) any action taken by the Guarantee Trustee or its agents hereunder
     shall bind the Holders, and the signature of the Guarantee Trustee or its
     agents alone shall be sufficient and effective to perform any such action;
     and no third party shall be required to inquire as to the authority of the
     Guarantee Trustee to so act, or as to its compliance with any of the terms
     and provisions of this Guarantee Agreement, both of which shall be
     conclusively evidenced by the Guarantee Trustee's or its agent's taking
     such action.

     SECTION 3.03 Not Responsible for Recitals or Issuance of Guarantee.

         The recitals contained in this Guarantee Agreement shall be taken as
the statements of the Guarantor, and the Guarantee Trustee does not assume any
responsibility for their correctness. The Guarantee Trustee makes no
representations as to the validity or sufficiency of this Guarantee Agreement.


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<PAGE>   14

     SECTION 3.04 The Guarantee Trustee May Own Preferred Securities.

         The Guarantee Trustee, in its individual or any other capacity, may
become the owner or pledgee of Preferred Securities and may otherwise deal with
the Guarantor with the same rights it would have if it were not the Guarantee
Trustee.

     SECTION 3.05 Moneys Received by the Guarantee Trustee to Be Held in Trust
Without Interest.

         All moneys received by the Guarantee Trustee in respect of Guarantee
Payments shall, until used or applied as herein provided, be held in trust for
the purposes for which they were received, but need not be segregated from other
funds except to the extent required by law. The Guarantee Trustee shall be under
no liability for interest on any moneys received by it hereunder except such as
it may agree in writing to pay thereon.

     SECTION 3.06 Compensation and Expenses of Guarantee Trustee.

         The Guarantor covenants and agrees to pay to the Guarantee Trustee from
time to time, and the Guarantee Trustee shall be entitled to, such compensation
as the Guarantor and the Guarantee Trustee shall from time to time agree in
writing (which shall not be limited by any provision of law in regard to the
compensation of a Guarantee Trustee of an express trust) for all services
rendered by it in the exercise and performance of any of the powers and duties
hereunder of the Guarantee Trustee, and the Guarantor will pay or reimburse the
Guarantee Trustee upon its request for all reasonable expenses, disbursements
and advances incurred or made by the Guarantee Trustee in accordance with any of
the provisions of this Guarantee Agreement (including the reasonable
compensation and the reasonable expenses and disbursements of its counsel and of
all persons not regularly in its employ) except any such expense, disbursement
or advance as may arise from its negligence or willful misconduct. The Guarantor
also covenants to indemnify each of the Guarantee Trustee or any predecessor
Guarantee Trustee and their officers, agents, directors and employees for, and
to hold them harmless against, any and all loss, liability, damage, claim or
expense including taxes (other than taxes based upon, measured by or determined
by the income, profit, franchise or doing business of the Guarantee Trustee)
incurred without negligence or willful misconduct on the part of the Guarantee
Trustee and arising out of or in connection with the acceptance or
administration of this trust, including the reasonable costs and expenses of
defending itself against any claim (whether asserted by the Guarantor, any
Holder or any other Person) of liability in the premises. The provisions of this
Section 3.06 shall survive the termination of this Guarantee Agreement and
resignation or removal of the Guarantee Trustee.



                                       11

<PAGE>   15

                                   ARTICLE IV
                                GUARANTEE TRUSTEE

     SECTION 4.01 Qualifications.

          There shall at all times be a Guarantee Trustee that shall:

          (i) not be an Affiliate of the Guarantor; and

          (ii) be a national banking association or corporation organized and
     doing business under the laws of the United States of America or any State
     or Territory thereof or of the District of Columbia, or a corporation or
     Person permitted by the Commission to act as an institutional trustee under
     the Trust Indenture Act, authorized under such laws to exercise corporate
     trust powers, having a combined capital and surplus of at least
     $50,000,000, and subject to supervision or examination by Federal, State,
     Territorial or District of Columbia authority. If such corporation
     publishes reports of condition at least annually, pursuant to law or to the
     requirements of the supervising or examining authority referred to above,
     then for the purposes of this clause (ii), the combined capital and surplus
     of such corporation shall be deemed to be its combined capital and surplus
     as set forth in its most recent report of condition so published.

         If at any time the Guarantee Trustee shall cease to satisfy the
requirements of clauses (i) and (ii) above, the Guarantee Trustee shall
immediately resign in the manner and with the effect set out in Section 4.02. If
the Guarantee Trustee has or shall acquire any "conflicting interest" within the
meaning of Section 310(b) of the Trust Indenture Act, the Guarantee Trustee and
the Guarantor shall in all respects comply with the provisions of Section 310(b)
of the Trust Indenture Act.

     SECTION 4.02 Appointment, Removal and Resignation of the Guarantee Trustee.

         (a) Subject to Section 4.02(b), the Guarantee Trustee may be appointed
or removed without cause at any time by the Guarantor.

         (b) The Guarantee Trustee shall not be removed in accordance with
Section 4.02(a) until a Successor Guarantee Trustee possessing the
qualifications to act as Guarantee Trustee under Section 4.01 has been appointed
and has accepted such appointment by written instrument executed by such
Successor Guarantee Trustee and delivered to the Guarantor and the Guarantee
Trustee being removed.

         (c) The Guarantee Trustee appointed to office shall hold office until
its successor shall have been appointed or until its removal or resignation.

         (d) The Guarantee Trustee may resign from office (without need for
prior or subsequent accounting) by an instrument (a "Resignation Request") in
writing signed by the



                                       12

<PAGE>   16

Guarantee Trustee and delivered to the Guarantor, which resignation shall take
effect upon such delivery or upon such later date as is specified therein;
provided, however, that no such resignation of the Guarantee Trustee shall be
effective until a Successor Guarantee Trustee possessing the qualifications to
act as Guarantee Trustee under Section 4.01 has been appointed and has accepted
such appointment by instrument executed by such Successor Guarantee Trustee and
delivered to the Guarantor and the resigning Guarantee Trustee.

         (e) If no Successor Guarantee Trustee shall have been appointed and
accepted appointment as provided in this Section 4.02 within 60 days after
delivery to the Guarantor of a Resignation Request or receipt of a notice of
removal by the Guarantee Trustee, the Guarantee Trustee resigning or to be
removed may, at the expense of the Guarantor petition any court of competent
jurisdiction for appointment of a Successor Guarantee Trustee. Such court may
thereupon after such notice, if any, as it may deem proper, appoint a Successor
Guarantee Trustee.


                                    ARTICLE V
                                    GUARANTEE

     SECTION 5.01 Guarantee.

         The Guarantor irrevocably and unconditionally agrees to pay in full to
the Holders the Guarantee Payments (without duplication of amounts theretofore
paid by the Issuer), as and when due, regardless of any defense, right of
set-off or counterclaim which the Issuer may have or assert. The Guarantor's
obligation to make a Guarantee Payment may be satisfied by direct payment of the
required amounts by the Guarantor to the Holders or to the Guarantee Trustee for
remittance to the Holders or by causing the Issuer to pay such amounts to the
Holders.

     SECTION 5.02 Waiver of Notice.

         The Guarantor hereby waives notice of acceptance of this Guarantee
Agreement and of any liability to which it applies or may apply, presentment,
demand for payment, any right to require a proceeding first against the Issuer
or any other Person before proceeding against the Guarantor, protest, notice of
nonpayment, notice of dishonor, notice of redemption and all other notices and
demands. Notwithstanding anything to the contrary herein, the Guarantor retains
all of its rights under the Indenture to extend the interest payment period on
the Notes and the Guarantor shall not be obligated hereunder to make any
Guarantee Payment during any Extension Period with respect to the Distributions
on the Preferred Securities.

     SECTION 5.03 Obligations Not Affected.

         The obligations, covenants, agreements and duties of the Guarantor
under this Guarantee Agreement shall in no way be affected or impaired by reason
of the happening from time to time of any of the following:


                                       13

<PAGE>   17

          (a) the release or waiver, by operation of law or otherwise, of the
     performance or observance by the Issuer of any express or implied
     agreement, covenant, term or condition relating to the Preferred Securities
     to be performed or observed by the Issuer;

          (b) the extension of time for the payment by the Issuer of all or any
     portion of the Distributions (other than an extension of time for payment
     of Distributions that result from any Extension Period), Redemption Price,
     Liquidation Distribution (as defined in the Declaration) or any other sums
     payable under the terms of the Preferred Securities or the extension of
     time for the performance of any other obligation under, arising out of, or
     in connection with, the Preferred Securities (other than an extension of
     time for payment of Distributions that result from any Extension Period);

          (c) any failure, omission, delay or lack of diligence on the part of
     the Guarantee Trustee or the Holders to enforce, assert or exercise any
     right, privilege, power or remedy conferred on the Guarantee Trustee or the
     Holders pursuant to the terms hereof or of the Preferred Securities,
     respectively, or any action on the part of the Issuer granting indulgence
     or extension of any kind;

          (d) the voluntary or involuntary liquidation, dissolution, sale of any
     collateral, receivership, insolvency, bankruptcy, assignment for the
     benefit of creditors, reorganization, arrangement, composition or
     readjustment of debt of, or other similar proceedings affecting, the Issuer
     or any of the assets of the Issuer;

          (e) any invalidity of, or defect or deficiency in, the Preferred
     Securities;

          (f) the settlement or compromise of any obligation guaranteed hereby
     or hereby incurred; or

          (g) any other circumstance whatsoever that might otherwise constitute
     a legal or equitable discharge or defense of a guarantor, it being the
     intent of this Section 5.03 that the obligations of the Guarantor with
     respect to the Guarantee Payments shall be absolute and unconditional under
     any and all circumstances.

         There shall be no obligation of the Guarantee Trustee or the Holders to
give notice to, or obtain consent of, the Guarantor with respect to the
happening of any of the foregoing.

     SECTION 5.04 Enforcement of Guarantee.

         The Guarantor and the Guarantee Trustee expressly acknowledge and agree
that (i) this Guarantee Agreement will be deposited with the Guarantee Trustee
to be held for the benefit of the Holders; (ii) the Guarantee Trustee has the
right to enforce this Guarantee Agreement on behalf of the Holders; (iii)
Holders representing not less than a Majority of Outstanding Preferred
Securities have the right to direct the time, method and place of conducting any
proceeding for any


                                       14

<PAGE>   18

remedy available to the Guarantee Trustee in respect of this Guarantee Agreement
or exercising any trust or other power conferred upon the Guarantee Trustee
under this Guarantee Agreement; and (iv) if the Guarantee Trustee fails to
enforce this Guarantee Agreement as provided in clauses (ii) and (iii) above,
any Holder may institute a legal proceeding directly against the Guarantor to
enforce its rights under this Guarantee Agreement, without first instituting a
legal proceeding against the Issuer, the Guarantee Trustee or any other Person.
Notwithstanding the foregoing, if the Guarantor has failed to make a Guarantee
Payment, a Holder may directly institute a proceeding against the Guarantor for
enforcement of this Guarantee Agreement for such payment without first
instituting a legal proceeding against the Issuer, the Guarantee Trustee or any
other Person.

     SECTION 5.05 Guarantee of Payment.

         This Guarantee Agreement creates a guarantee of payment and not merely
of collection. This Guarantee Agreement will not be discharged except by payment
of the Guarantee Payments in full (without duplication of amounts theretofore
paid by the Issuer) or upon the distribution of the Notes to the Holders as
provided in the Declaration.

     SECTION 5.06 Subrogation.

         The Guarantor shall be subrogated to all (if any) rights of the Holders
against the Issuer in respect of any amounts paid to the Holders by the
Guarantor under this Guarantee Agreement; provided, however, that the Guarantor
shall not (except to the extent required by mandatory provisions of law) be
entitled to enforce or exercise any rights which it may acquire by way of
subrogation or any indemnity, reimbursement or other agreement, in all cases as
a result of payment under this Guarantee Agreement, if, at the time of any such
payment, any amounts are due and unpaid under this Guarantee Agreement. If any
amount shall be paid to the Guarantor in violation of the preceding sentence,
the Guarantor agrees to hold such amount in trust for the Holders and to pay
over such amount to the Holders or to the Guarantee Trustee for remittance to
the Holders.

     SECTION 5.07 Independent Obligations.

         The Guarantor acknowledges that its obligations hereunder are
independent of the obligations of the Issuer with respect to the Preferred
Securities and that the Guarantor shall be liable as principal and as debtor
hereunder to make Guarantee Payments pursuant to the terms of this Guarantee
Agreement notwithstanding the occurrence of any event referred to in subsections
(a) through (g), inclusive, of Section 5.03 hereof.


                                       15

<PAGE>   19

                                   ARTICLE VI
                    LIMITATION OF TRANSACTIONS; SUBORDINATION

     SECTION 6.01 Limitation of Transactions.

         So long as any Preferred Securities remain outstanding, the Guarantor
shall not (a) make any payment of principal, interest or premium, if any, on or
repay, repurchase or redeem any debt securities that rank junior to the Notes in
the right of payment issued by the Guarantor, or (b) make any guarantee payments
with respect to any guarantee by the Guarantor of any securities of any of its
subsidiaries if such guarantee ranks junior to the Notes in the right of payment
or (c) declare or pay any dividends or distributions on, or redeem, purchase,
acquire or make a liquidation payment with respect to, any of the Guarantor's
capital stock, except for or as a result of (i) dividends or distributions in,
or options, warrants or rights to subscribe for or purchase, the Guarantor's
common stock; (ii) any declaration of a dividend in connection with the
implementation of a shareholder's rights plan, or the issuance of shares under
any such plan in the future, or the redemption or repurchase of any such rights
pursuant thereto; (iii) a reclassification of the Guarantor's capital stock
solely into shares of one or more classes or series of the Guarantor's capital
stock or the exchange or conversion of one class or series of the Guarantor's
capital stock for or into another class or series of the Guarantor's capital
stock; (iv) the purchase of fractional interests in shares of the Guarantor's
capital stock pursuant to the conversion or exchange provisions of such capital
stock or the security being converted or exchanged; and (v) the purchase of the
Guarantor's common stock in connection with the Guarantor's normal course issuer
bid-purchases for the satisfaction by the Guarantor of its obligations under any
benefit plans for the Guarantor and the Guarantor's subsidiaries' directors,
officers or employees or under any of the Guarantor's dividend reinvestment
plans, if at such time (i) the Guarantor shall be in default with respect to its
Guarantee Payments or other payment obligations hereunder, (ii) there shall have
occurred and be continuing any event of default under the Declaration or (iii)
the Guarantor shall have given notice of its election of an Extension Period and
such period, or any extension thereof, is continuing. In addition, so long as
any Preferred Securities remain outstanding, the Guarantor (i) will remain the
sole direct or indirect owner of all of the outstanding Common Securities and
shall not cause or permit the Common Securities to be transferred except to the
extent such transfer is permitted under the Declaration; provided that any
permitted successor of the Guarantor under the Indenture may succeed to the
Guarantor's direct or indirect ownership of the Common Securities, (ii) will
cause the holder of the Common Securities to satisfy the requirements of Section
5.3 of the Declaration and (iii) will use reasonable efforts to cause the Issuer
to continue to be treated as a grantor trust for United States federal income
tax purposes, except in connection with a distribution of Notes as provided in
the Declaration.

     SECTION 6.02 Subordination.

         If a Trust Enforcement Event has occurred and is continuing under the
Declaration the rights of the holders of the Common Securities to receive
Guarantee Payments will be subordinated to the rights of the Holders of the
Preferred Securities to receive Guarantee Payments.



                                       16

<PAGE>   20

                                  ARTICLE VII
                                  TERMINATION

     SECTION 7.01 Termination.

         This Guarantee Agreement shall terminate and be of no further force and
effect (i) upon full payment of the Redemption Price of all Preferred
Securities, (ii) upon the distribution of Notes to Holders and holders of Common
Securities in exchange for all of the Preferred Securities and Common Securities
or (iii) upon full payment of the amounts payable in accordance with the
Declaration upon liquidation of the Issuer. Notwithstanding the foregoing, this
Guarantee Agreement will continue to be effective or will be reinstated, as the
case may be, if at any time any Holder must restore payment of any sums paid
with respect to the Preferred Securities or under this Guarantee Agreement.


                                  ARTICLE VIII
                    LIMITATION OF LIABILITY; INDEMNIFICATION

     SECTION 8.01 Exculpation.

         (a) No Indemnified Person shall be liable, responsible or accountable
in damages or otherwise to the Guarantor or any Holder for any loss, damage or
claim incurred by reason of any act or omission performed or omitted by such
Indemnified Person in good faith in accordance with this Guarantee Agreement and
in a manner such Indemnified Person reasonably believed to be within the scope
of the authority conferred on such Indemnified Person by this Guarantee
Agreement or by law, except that an Indemnified Person shall be liable for any
such loss, damage or claim incurred by reason of such Indemnified Person's
negligence or willful misconduct with respect to such acts or omissions.

         (b) An Indemnified Person shall be fully protected in relying in good
faith upon the records of the Guarantor and upon such information, opinions,
reports or statements presented to the Guarantor by any Person as to matters the
Indemnified Person reasonably believes are within such other Person's
professional or expert competence and who has been selected with reasonable care
by or on behalf of the Guarantor, including information, opinions, reports or
statements as to the value and amount of the assets, liabilities, profits,
losses or any other facts pertinent to the existence and amount of assets from
which Distributions to Holders might properly be paid.

     SECTION 8.02 Indemnification.

         To the fullest extent permitted by applicable law, the Guarantor shall
indemnify and hold harmless each Indemnified Person from and against any loss,
damage or claim incurred by such Indemnified Person by reason of any act or
omission performed or omitted by such Indemnified Person in good faith in
accordance with this Guarantee Agreement and in a manner such Indemnified


                                       17

<PAGE>   21
Person reasonably believed to be within the scope of authority conferred on
such Indemnified Person by this Guarantee Agreement, except that no Indemnified
Person shall be entitled to be indemnified in respect of any loss, damage or
claim incurred by such Indemnified Person by reason of negligence or willful
misconduct with respect to such acts or omissions.

     SECTION 8.03 Survive Termination.

         The provisions of Sections 8.01 and 8.02 shall survive the termination
of this Guarantee Agreement or the resignation or removal of the Guarantee
Trustee.


                                   ARTICLE IX
                                  MISCELLANEOUS

     SECTION 9.01 Successors and Assigns.

         All guarantees and agreements contained in this Guarantee Agreement
shall bind the successors, assignees, receivers, trustees and representatives of
the Guarantor and shall inure to the benefit of the Guarantee Trustee and the
Holders then outstanding. Except in connection with a consolidation, merger or
sale involving the Guarantor that is permitted under Article X of the Indenture,
the Guarantor shall not assign its obligations hereunder.

     SECTION 9.02 Amendments.

         Except with respect to any changes which do not adversely affect the
rights of Holders in any material respect (in which case no consent of Holders
will be required), this Guarantee Agreement may only be amended with the prior
approval of the Guarantor, the Guarantee Trustee and the Holders of not less
than a Majority of Outstanding Preferred Securities. The provisions of Section
11.2 of the Declaration concerning meetings of Holders shall apply to the giving
of such approval.

     SECTION 9.03 Notices.

         Any notice, request or other communication required or permitted to be
given hereunder shall be in writing, in English, duly signed by the party giving
such notice, and delivered, telecopied or mailed by first class mail as follows:



                                       18

<PAGE>   22

          (a) if given to the Guarantor, to the address set forth below or such
     other address as the Guarantor may give notice of to the Holders:

           Valero Energy Corporation
           One Valero Place
           P.O. Box 500
           San Antonio, Texas 78212
           Attention:  Jay D. Browning, Corporate Secretary
           Facsimile:  (210) 370-2988

     with a copy to:

           Attention:  Donna M. Titzman
           Facsimile:  (210) 370-2497

          (b) if given to the Guarantee Trustee, to the address set forth below
     or such other address as the Guarantee Trustee may give notice of to the
     Holders:

           The Bank of New York
           101 Barclay Street
           21 West
           New York, New York 10286
           Attention: Corporate Trust Trustee Administration
           Facsimile:  (212) 815-5915

          (c) if given to any Holder, at the address set forth on the books and
     records of the Issuer.

         All notices hereunder shall be deemed to have been given when (i)
received in person, (ii) telecopied with receipt confirmed, or (iii) mailed by
first class mail, postage prepaid, when received, except that if a notice or
other document is refused delivery or cannot be delivered because of a changed
address of which no notice was given, such notice or other document shall be
deemed to have been delivered on the date of such refusal or inability to
deliver.

     SECTION 9.04 Genders.

         The masculine, feminine and neuter genders used herein shall include
the masculine, feminine and neuter genders.

     SECTION 9.05 Benefit.

         This Guarantee Agreement is solely for the benefit of the Guarantee
Trustee and the Holders and, subject to Section 3.01(a), is not separately
transferable from the Preferred Securities.


                                       19

<PAGE>   23

     SECTION 9.06 Governing Law.

         THIS GUARANTEE AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK (WITHOUT REGARD
TO PRINCIPLES OF CONFLICTS OF LAWS).

     SECTION 9.07 Counterparts.

         This Guarantee Agreement may be executed in counterparts, each of which
shall be an original; but such counterparts shall together constitute one and
the same instrument.

     SECTION 9.08 Exercise of Overallotment Option.

         If and to the extent that Preferred Securities are issued by the Issuer
upon exercise of the overallotment option referred to in the first WHEREAS
clause, the Guarantor agrees to give prompt notice thereof to the Guarantee
Trustee but the failure to give such notice shall not relieve the Guarantor of
any of its obligations hereunder.

     SECTION 9.09 Limited Liability.

         Neither the Guarantee Trustee nor the Holders, in their capacities as
such, shall be personally liable for any liabilities or obligations of the
Guarantor arising out of this Guarantee Agreement. The parties further hereby
agree that the Holders, in their capacities as such, shall be entitled to the
same limitation of personal liability extended to the stockholders of private
corporations for profit organized under the General Corporation Law of the State
of Delaware.



                                       20

<PAGE>   24

     THIS GUARANTEE AGREEMENT is executed as of the day and year first above
written.

                        VALERO ENERGY CORPORATION


                        By:
                            ------------------------------------------------
                            John D. Gibbons, Vice President
                            and Chief Financial Officer


                        THE BANK OF NEW YORK
                            as Guarantee Trustee


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



                                       21