<PAGE>
                                                                    EXHIBIT 10.1

                              INSTRUMENT AMENDING
                         LYONDELL PETROCHEMICAL COMPANY
                      EXECUTIVE SUPPLEMENTARY SAVINGS PLAN



     LYONDELL PETROCHEMICAL COMPANY hereby amends the Lyondell Petrochemical
Company Executive Supplementary Savings Plan, to read in its entirety as the
document entitled
"Lyondell Petrochemical Company Executive Supplementary Savings Plan, Edition of
January 1, 1997", as attached hereto.

     IN WITNESS WHEREOF, LYONDELL PETROCHEMICAL COMPANY, acting by and through
its duly authorized officer, has caused this Instrument to be executed on this
21st of February, 1997.



ATTEST:                             LYONDELL PETROCHEMICAL COMPANY



/s/ Gerald O'Brien                  By:/s/ Richard W. Park
----------------------                 --------------------------
Assistant Secretary                      Richard W. Park
                                         Vice President, Human Resources

                                       1
<PAGE>
 
                         LYONDELL PETROCHEMICAL COMPANY
                      EXECUTIVE SUPPLEMENTARY SAVINGS PLAN
                           EDITION OF JANUARY 1, 1997

                                       1
<PAGE>
 
                               TABLE OF CONTENTS
                               -----------------
<TABLE>
<CAPTION>
                                                             PAGE
                                                             ----
<S>          <C>                                             <C>
Section 1. Intent of Plan..................................     1

Section 2. Effective Date of Plan.........................      1

Section 3. Definitions.....................................     1
     3.1     "Administrative Committee" or "Committee".....     1
     3.2     "Base Pay"....................................     1
     3.3     "Company".....................................     1
     3.4     "Company Contribution"........................     1
     3.5     "Disability" or Disabled".....................     1
     3.6     "Employee"....................................     2
     3.7     "Plan Year"...................................     2
     3.8     "Savings Contribution"........................     2
 
Section 4.  Costs of Plan..................................     2
 
Section 5.  Eligibility for Benefits.......................     2
 
Section 6.  Amount of Benefit..............................     3
 
Section 7.  Crediting of Benefit...........................     3
 
Section 8.  Time of Payment of Benefit.....................     3
 
Section 9.  Death Benefits.................................     3
 
Section 10. Administration................................      4
     10.1    Rules of Conduct..............................     4
     10.2    Legal, Accounting, Clerical 
              and Other Services...........................     4
     10.3    Interpretation of Provisions..................     4
     10.4    Records of Administration.....................     4
     10.5    Denial of Claim...............................     4
     10.6    Liability of Committee........................     4
 
Section 11. Facility of Payment and 
              Lapse of Benefits............................     4
     11.1    Provisions for Incapacity.....................     4
     11.2    Payments or Deposits..........................     5
 
Section 12. General Provisions............................      5
     12.1    Unfunded Benefit Plan.........................     5
     12.2    Payments and Benefits Not Assignable..........     5
     12.3    No Right of Employment........................     5
     12.4    Adjustments...................................     5
 
Section 13. Amendments and Discontinuance.................      5
     13.1    Amendment of Plan.............................     5
     13.2    Termination...................................     5
     13.3    Effect of Amendment or Termination............     5
</TABLE>

                                       2
<PAGE>
 
                        LYONDELL PETROCHEMICAL COMPANY
                     EXECUTIVE SUPPLEMENTARY SAVINGS PLAN



                          SECTION 1.  INTENT OF PLAN.

     1.1  This Plan is intended to provide an annual benefit, in accordance with
its provisions to that select group of management or highly compensated
employees excluded from making Savings Contributions and from receiving Company
Contributions in the Lyondell Petrochemical Company 401(k) and Savings Plan due
to the probability that their benefits under one or more qualified employee
pension benefit plans maintained by Lyondell Petrochemical Company might be
reduced because of the maximum annual limitations on contributions and benefits
imposed by Sections 415, 401 or other Sections of the Internal Revenue Code of
1986, as amended (the "Code").


                      SECTION 2. EFFECTIVE DATE OF PLAN.

     2.1  This Plan shall be effective as of January 1, 1997.


                            SECTION 3. DEFINITIONS

     3.1  "Administrative Committee" or "Committee" means the Benefits
Administrative Committee appointed by the Compensation Committee of the Board of
Directors of the Company.

     3.2  "Base Pay" means an Employee's regular wages or salary, as determined
by the Company, excluding extra pay, such as bonuses, or other supplementary
allowances;

     3.3  "Company" means Lyondell Petrochemical Company and any of its
subsidiaries or affiliates whose employees are included in this Plan upon
authorization of the Board of Directors of Lyondell Petrochemical Company or the
Compensation Committee of the Board of Directors, pursuant to delegation from
the Board of Directors.

     3.4  "Company Contribution" means contributions made by the Company on a
participant's behalf under the Company's 401(k) and Savings Plan.

     3.5  "Disability" or Disabled" means an Employee's total and permanent
disability, as determined by the Administrative Committee.
<PAGE>
 
     3.6  "Employee" means any person who:

          (a)  is regularly employed by the Company on a full time or part time
               basis;

          and

          (b)  either:

               (i)  is a member of that select group of management or highly
                    compensated employees on the executive payroll; or

               (ii) is an employee with an annual Base Pay no less than
                    $150,000;

               and

          (c)  has been excluded from making Savings Contributions and from
               receiving Company Contributions under the Lyondell Petrochemical
               Company 401(k) and Savings Plan because of the Company's
               determination that the maximum annual contribution and benefit
               limitations imposed by the Code potentially will apply to the
               Employee.

     3.7  "Plan Year" means the calendar year..

     3.8  "Savings Contribution" means a participant's after-tax contributions
to the Company's 401(k) and Savings Plan.


                          SECTION 4.  COSTS OF PLAN.

     4.1  The Company shall bear all costs of this Plan, including its
administration, and no Employee contributions shall be required or permitted.


                     SECTION 5.  ELIGIBILITY FOR BENEFITS.

     5.1  Each person who qualifies as an Employee under Paragraph 3.6 for all
or any part of a Plan Year shall participate in the Plan for that portion of the
Plan Year.

                                       2
<PAGE>
 
                         SECTION 6.  AMOUNT OF BENEFIT.

     6.1  The amount of an Employee's benefit for each Plan Year shall be
equal to either:

         (a)   An amount equal to the maximum Company Contribution under the
               Lyondell Petrochemical Company 401(k) and Savings Plan, assuming
               no limitations on contributions imposed by Section 415 or any
               other Sections of the Code during the Plan Year, if an Employee
               makes an elective deferral of at least 5% of Base Pay or the
               maximum permissible elective deferral, whichever is less, under
               the Lyondell Petrochemical Company 401(k) and Savings Plan for
               the Plan Year, or

         (b)   An amount equal to 1.6 times the amount of elective deferrals
               made by the Employee under the Lyondell Petrochemical Company
               401(k) and Savings Plan, if an Employee does not make an elective
               deferral of at least 5% of Base Pay or the maximum permissible
               elective deferral under the Lyondell Petrochemical Company 401(k)
               and Savings Plan for the Plan Year.


                       SECTION 7.  CREDITING OF BENEFIT.

     7.1  The Administrative Committee shall determine the amount of benefit to
be credited to an Employee for a Plan Year within 30 days after the end of the
Plan Year or 30 days after the Employee's termination of employment, whichever
occurs earlier.


                    SECTION 8.  TIME OF PAYMENT OF BENEFIT.

     8.1  An Employee shall be paid the benefit to which the Employee is
entitled for a Plan Year in a single cash payment within 30 days following the
date the Company credits the benefit, unless the benefit has been deferred under
the Lyondell Petrochemical Company Executive Deferral Plan.


                          SECTION 9.  DEATH BENEFITS.

     9.1  If an Employee dies prior to payment of the benefit due under the
Plan, the benefit shall be paid as soon as practicable following the Employee's
death to the Employee's most recently designated beneficiary or beneficiaries.
The beneficiary must be designated in writing on a form approved by the
Committee and must be accepted by the Plan prior to the Employee's death.  If no
designation has been made, or if all designated beneficiaries have died before
the Employee, the benefit shall be paid to the Employee's estate.

                                       3
<PAGE>
 
                          SECTION 10. ADMINISTRATION.

     10.1 Rules of Conduct.  The Administrative Committee shall adopt rules to
          ----------------                                                    
conduct its business and the Plan's administration as it considers desirable,
provided they do not conflict with the Plan's provisions.

     10.2 Legal, Accounting, Clerical and Other Services.  The Administrative
          ----------------------------------------------                     
Committee may authorize one or more of its members or any agent to act on its
behalf and may contract for legal, accounting, clerical and other services to
carry out this Plan.  The Company shall pay all expenses of the Administrative
Committee.

     10.3 Interpretation of Provisions.  The Administrative Committee shall have
          ----------------------------                                          
the exclusive right and discretionary authority to interpret the provisions of
this Plan and to decide questions arising in its administration including, but
not limited to, questions of eligibility for benefits under this Plan.  The
decisions and interpretations of the Administrative Committee shall be final,
binding and conclusive on the Company, its Employees and all other persons.

     10.4 Records of Administration.  The Administrative Committee shall
          -------------------------                                     
maintain Plan administration records.  These records are subject to audit by the
Company.

     10.5 Denial of Claim.  The Administrative Committee shall provide adequate
          ---------------                                                      
written notice to any Employee or beneficiary whose claim for benefits under
this Plan has been denied, setting forth the specific reasons for the denial.
The Administrative Committee will give the Employee or beneficiary an
opportunity for a full and fair review of the decision denying the claim.  The
Employee or beneficiary shall have 60 days from the date of the notice denying
the claim to request a full and fair review.

     10.6 Liability of Committee.  No member of the Administrative Committee
          ----------------------                                            
shall be liable for any action taken in good faith or for exercising any power
given to the Administrative Committee or for the actions of other Committee
members.


            SECTION 11.  FACILITY OF PAYMENT AND LAPSE OF BENEFITS.

     11.1 Provision for Incapacity.  If the Administrative Committee deems that
          ------------------------                                             
any person entitled to receive any payment under this Plan is incapable of
receiving or disbursing the payment because of minority, illness or infirmity,
mental incompetency, or incapacity of any kind, the Committee, in its sole
discretion, may take any one or more of the following actions:  it may apply the
payment directly for the person's comfort, support and maintenance; it may
reimburse any other person for support supplied to the person entitled to
receive any payment; or it may pay the payment to any other person the Committee
selects to disburse the payment for the comfort, support and maintenance of the
person entitled to the payment, including, without limitation, to any relative
who has wholly or partially undertaken the expense of the person's comfort, care
and maintenance, or any institution which is caring for or which has custody

                                       4
<PAGE>
 
of the person entitled to the payment.  The Administrative Committee, in its
sole discretion, may deposit any payment due to a minor to the minor's credit in
any savings or commercial bank of the Committee's choice.

     11.2 Payments or Deposits.  Payments or deposits made under this Section 11
          --------------------                                                  
shall completely discharge, to the extent of the payment, all liability of the
Administrative Committee, the Company and this Executive Supplementary Savings
Plan under this Plan or otherwise.  A person's receipt of any payment,
distribution or deposit shall be a complete acquittance and there shall be no
liability to see to the application of any payments, distributions or deposits
made.


                       SECTION 12.  GENERAL PROVISIONS.

     12.1 Unfunded Benefit Plan.  This Executive Supplementary Savings Plan is
          ---------------------                                               
intended to be an unfunded plan maintained primarily for the purpose of
providing deferred compensation to a select group of management or highly
compensated employees.

     12.2 Payments and Benefits Not Assignable.  Benefits under this Plan are
          ------------------------------------                               
not assignable, transferable or subject to alienation by Employees.  Likewise,
payments are not subject to attachment by creditors of, or through legal process
against, the Company, the Administrative Committee, or any Employee.

     12.3 No Right of Employment.  The provisions of this Plan shall not give an
          ----------------------                                                
Employee the right to be retained in the Company's service nor shall this Plan
or any action taken under it be construed as an employment contract.

     12.4 Adjustments.  At the Company's request, the Administrative Committee,
          -----------                                                          
may adjust an Employee's benefit under this Plan or make other adjustments with
respect to the Employee as required to correct administrative errors or provide
uniform treatment of Employees in a manner consistent with this Plan's intent
and purpose.


                  SECTION 13.  AMENDMENTS AND DISCONTINUANCE.

     13.1 Amendment of Plan.  This Plan may be amended from time to time by the
          -----------------                                                    
Compensation Committee of the Board of Directors of the Company.

     13.2 Termination.  The Compensation Committee of the Board of Directors
          -----------                                                       
reserves the right to terminate this Plan at any time.

     13.3 Effect of Amendment or Termination.  No Plan amendment or Plan
          ----------------------------------                            
termination may adversely affect the benefit payable to any Employee entitled to
receive benefits under this Plan prior to the effective date of the amendment or
termination.

                                       5