EXHIBIT 10.4

William  R.  Klesse______________________  ("Executive")  and  Ultramar  Diamond
Shamrock Corporation, a Delaware corporation (the "Company"),  hereby enter into
this Second Amendment to Employment  Agreement between Executive and the Company
and dated October 23, 1996_____________________, and effective as of December 3,
1996_____________________ (the "Employment Agreement"), as amended.

WHEREAS the Executive and the Company  entered into the Employment  Agreement as
of the date stated above; and

WHEREAS Section 12.8 of the Employment Agreement provides that it may be amended
only by an  instrument  in writing  approved  by the  Company  and signed by the
Executive and the Company; and

WHEREAS the Company and Executive wish to amend the Employment  Agreement to add
certain  provisions  approved  by the  Compensation  Committee  of the  Board of
Directors of the Company effective as of September 6, 2000.

NOW, THEREFORE,  in consideration of the promises and mutual covenants contained
herein and in the  Employment  Agreement,  it is agreed  that,  effective  as of
September 6, 2000, the Employment Agreement is amended as follows:

                                       I.

The first  sentence of Section 2.1 is deleted and the  following is  substituted
for it:

         During the Term,  the Executive  will serve as the Company's  Executive
         Vice  President  Operations_____________________  and  will  have  such
         duties,   functions,   responsibilities,   and  authority  as  are  (i)
         consistent  with the  Executive's  position as Executive Vice President
         Operations________________________  of the Company; or (ii) assigned to
         his office in the Company's bylaws; or (iii) reasonably assigned to him
         by the Company's Board of Directors (the "Board").

                                       II.

The first sentence of Section 3 is deleted and the following is substituted  for
it:

         In connection  with his employment  during the Term,  unless  otherwise
         agreed by the  Executive,  the Executive will be based at the Company's
         facility  currently  known as the Avon  Refinery,  located in Martinez,
         California.


                                      III.

Sections 4.1(i) and (ii) are deleted and the following substituted for them:

         (i)  Annual Base Salary and Cost of Living Adjustment.  During the Term
     of  this  Agreement,  the  Company will pay to the Executive an annual base
     salary of not less than  $420,000, which annual base salary may be modified
     from  time  to time by the Board (or the Compensation Committee thereof) in
     its sole discretion, payable at the times and in the manner consistent with
     the  Company's' general  policies  regarding  executive  employees' compen-
     sation.  Effective   with   the   first   payroll   period   following  the
     Executive's relocation  to  the  Avon  Refinery and  continuing  thereafter
     for ten  years  (provided Executive  remains  employed  by  the Company and
     located at the Avon Refinery),  the Company  will pay  Executive  a cost of
     living  adjustment ("COLA")  determined and payable as provided herein. For
     the duration of the first  year the COLA  shall be  $126,000.  On the first
     through  the ninth anniversary  of  the first COLA payment,  the COLA shall
     reduced  annually by $12,600.  For  example,  on the second anniversary the
     COLA  shall  be  $113,400;  on  the  third  anniversary  the  COLA shall be
     $100,800; subsequent years shall be reduced  in like  manner.  On the tenth
     anniversary the COLA shall be $12,600. On the eleventh anniversary the COLA
     shall be discontinued it its entirety.  The COLA shall  be  payable  at the
     times  and  in  the  manner consistent with Executive's annual base salary,
     provided, however, that, unless otherwise provided in this Agreement,  such
     COLA shall not be included for any compensation or benefits  plan or policy
     as  annual  base  salary  or  compensation,  including (but not limited to)
     computation of annual incentive eligible earnings, or as eligible compensa-
     tion for any qualified or nonqualified retirement plans of the Company. The
     Board (or the Compensation  Committee) may from time to time authorize such
     additional  compensation  to  the Executive, in cash or in property, as the
     Board may determine its sole discretion to be appropriate.


         (ii)  Annual Incentive Compensation.  If the Board (or the Compensation
     Committee thereof) authorizes any cash  incentive  compensation or approves
     any other management incentive program or  arrangement,  the Executive will
     be eligible to  participate in such plan,  program,  or  arrangement  under
     the  general  terms  and  conditions   applicable  executive and management
     employees;  provided,  however,  that Executive's "annual incentive factor"
     under any annual incentive  compensation  program  or arrangement shall not
     be less than 50% of his annual compensation  (excluding the COLA).  Nothing
     in this section  4.1(ii)  will  guarantee  to the  Executive  any  specific
     amount of incentive compensation, or prevent the Board (or the Compensation
     Committee  thereof) from  establishing  performance  goals and compensation
     targets applicable only to the Executive.

                                       IV.

Section  4.1 is  amended  by adding a new  subsection  (iii)  that shall read as
follows:

         (iii)  Relocation.  The Company shall relocate Executive  to  the  Avon
     Refinery  in  accordance  with the  provisions of the Company's  Relocation
     Guide updated  October 11, 2000, as enhanced for  relocations in connection
     with the Avon Refinery ("Relocation  Guide"),  a copy of which is  attached
     hereto as  Exhibit  "B." Such  Relocation  Guide shall  include (but is not
     limited to) benefits  such  as  Executive's  entitlement  to  an incidental
     moving expense  allowance of $105,000, and  an interest-free loan for up to
     $1,638,000 to  purchase  a  primary  residence,  each  such  benefit  to be
     governed  by  the  terms and  conditions  of the  Relocation  Guide and any
     applicable  agreements,  including but not limited to a Promissory Note and
     Deed of Trust. If Executive's employment is involuntarily  terminated other
     than for Cause as provided in Section 5.4(i) hereunder,  or is  voluntarily
     terminated as provided in Section 5.4(ii) as a result of Executive's death,
     Disability, or retirement during the term of this Agreement, in addition to
     all other rights and benefits of the Executive, the following  shall apply:
     at the  Executive's  election  in  writing  (or his spouse if Executive has
     died),  made within twelve months of the event,  the Company shall relocate
     the Executive and his  family to their  original location or other location
     of Executive's choice  within the contiguous 48 United States in accordance
     with  a  relocation   program at least as generous as the Relocation  Guide
     (but excluding entitlement to any COLA and interest-free loan).

                                       V.

Subsections  (1)  and (2) of  Section  5.5(i)(a)  shall  be  revised  to read as
follows:

     (i) Form and Amount.  Upon Executive's involuntary  termination, other than
for Cause, the Company shall:

         (a)  subject to Section 5.5(iii), pay or provide Executive

              (1)  his  annual  salary (including COLA)  and  benefits until the
         date of termination,

              (2)  within  five  business  days after any  revocation  period in
         the release  described  in Section  5.5(iii)  has expired,   a lump sum
         cash  payment  equal to  three  multiplied  by  the sum of (x) and (y),
         where (x) is  Executive's highest  annual  base salary  (including  any
         applicable  COLA) in effect during the three years prior to his date of
         termination,  and (y) is  the  highest  annual  incentive  compensation
         earned  by  Executive during the three years prior to his  termination;
         provided, however, that all amounts  received by Executive  pursuant to
         the Ultramar Diamond Shamrock  Corporation  Intermediate  Incentive and
         Performance-Based  Restricted  Stock  Plans  shall  not  be  considered
         "annual incentive compensation" for the purposes of this Section 5.5(i)
         (a)(2).

                                       VI.

Except as otherwise  provided  herein,  the Agreement shall remain in full force
and effect.

IN WITNESS  WHEREOF,  the parties have executed this Agreement as of the date of
September 6, 2000.

_____________________________________
Executive

ULTRAMAR DIAMOND SHAMROCK CORPORATION


By:__________________________________
     Chairman, President and CEO