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                                                                   EXHIBIT 10.18


                                    Amendment
                                       To
                Apache Corporation Money Purchase Retirement Plan

         Apache Corporation ("Apache") maintains the Apache Corporation Money
Purchase Retirement Plan (the "Plan"). In section 9.4 of the Plan, Apache
reserved the right to amend the Plan from time to time. Apache hereby exercises
such right by adding the following paragraph 3.1(a)(iv) to the Plan, effective
as of January 1, 1998.


                  (iv) Special Allocation for 1998. In addition to the
         allocation provided in paragraph (ii), the two eligible Participants
         who had the smallest "plan year compensation" (as defined below) in
         1998 shall receive an additional allocation of Company Mandatory
         Contributions equal to 3.138% of the eligible Participant's plan year
         compensation in 1998. For purposes of this paragraph only, "plan year
         compensation" means those amounts reported as "wages, tips, other
         compensation" on Form W-2 by the Company or an Affiliated Entity and
         elective contributions that are not includable in the Employee's income
         pursuant to Code section 125 or 402(e)(3).


                     EXECUTED this 21st day of October 1999.

                                       APACHE CORPORATION


                                       By: /s/ Daniel L. Schaeffer
                                          ------------------------------------
                                       Title: Vice President, Human Resources
                                             ---------------------------------


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                                    Amendment
                                       To
                Apache Corporation Money Purchase Retirement Plan

         Apache Corporation ("Apache") maintains the Apache Corporation Money
Purchase Retirement Plan (the "Plan"). Apache filed the Plan with the IRS on
September 15, 1998 in order to obtain a favorable determination as to the
qualified status of the Plan. The IRS granted the Plan a favorable determination
letter dated July 23, 1999, contingent on certain amendments being made to the
Plan. In section 9.4 of the Plan, Apache reserved the right to amend the Plan
from time to time. Apache hereby exercises such right as follows, effective as
of January 1, 1997.

1.       Section 1.12 shall be replaced in its entirety by the following.

         1.12 "Covered Employee" means any Employee of the Company, with the
         following exceptions.


                  (a) Any individual directly employed by an entity other than
         the Company shall not be a Covered Employee, even if such individual is
         considered a common-law employee of the Company or is treated as an
         employee of the Company pursuant to Code section 414(n).

                  (b) A non-resident alien shall not be a Covered Employee.

                  (c) An Employee included in a unit of Employees covered by a
         collective bargaining agreement shall not be a Covered Employee unless
         the collective bargaining agreement specifically provides for such
         Employee's participation in the Plan.

                  (d) An Employee whose job is classified as "temporary" shall
         be a Covered Employee only after he or she has worked for the Company
         and Affiliated Entities for six consecutive months.

                  (e) An Employee shall not be a Covered Employee while he or
         she is classified as an "intern," a "consultant," or an "independent
         contractor." An Employee may be classified as an "intern" only if he or
         she is currently enrolled (or the Company expects him or her to be
         enrolled within the next 12 months) in a high school, college, or
         university. An Employee may be classified as an intern even if he or
         she does not receive academic course credit from his or her school for
         this employment with the Company.

                  (f) An individual who is employed pursuant to a written
         agreement with an agency or other third party for a specific job
         assignment or project shall not be a Covered Employee.

2.       The last sentence of section 1.16 shall be replaced by the following
sentence.


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         The term "Employee" shall also include any individual who provides
         services to the Company or an Affiliated Entity pursuant to an
         agreement between the Company or an Affiliated Entity and a third party
         that employs the individual, but only if the individual has performed
         such services for the Company or an Affiliated Entity on a
         substantially full-time basis for at least one year and only if the
         services are performed under the primary direction or control by the
         Company or an Affiliated Entity; provided, however, that if the
         individuals included as Employees pursuant to the first part of this
         sentence constitute 20% or less of the Non-Highly Compensated Employees
         of the Company and Affiliated Entities, then any such individuals who
         are covered by a qualified plan that is a money purchase pension plan
         that provides a nonintegrated employer contribution rate for each
         participant of at least 10% of compensation, that provides for full and
         immediate vesting, and that provides immediate participation for each
         employee of the third party (other than those who perform substantially
         all of their services for the third party and other than those whose
         compensation from the third party during each of the four preceding
         plan years was less than $1000) shall not be considered an Employee.

3.       Section 1.20 shall be replaced in its entirety by the following.

         1.23 "Highly Compensated Employee" means, for each Plan Year, an
         Employee who (a) had Compensation of $80,000 (as adjusted by the
         Secretary of the Treasury) or more during the immediately preceding
         Plan Year, or (b) is a Five-Percent Owner during the current Plan Year,
         or (c) was a Five-Percent Owner during the immediately preceding Plan
         Year. The term "Highly Compensated Employee" shall also include, where
         the context so requires, any former Employee who was a Highly
         Compensated Employee when he or she separated from service with the
         Company and all Affiliated Entities, as well as any former Employee who
         was a Highly Compensated Employee at any time after attaining age 55.

4.       Subsection 6.1(c) shall be replaced in its entirety by the following.

                  (c) Waiver of QPSA.

                           (i) General. In order for the QPSA to be waived, the
                  Participant must be provided with an explanation of the QPSA
                  and then elect to waive the QPSA (which the Participant may do
                  by naming a beneficiary other than his or her Spouse) and the
                  Spouse must consent to the Participant's election.

                           (ii) Spouse's Consent. The Spouse's consent must be
                  in writing. The Spouse's signature must be witnessed by a
                  Committee member of by a notary public. The Spouse must
                  acknowledge the effect of the consent. The Spouse may limit
                  his or her consent to a specific beneficiary or may allow the
                  Participant to thereafter


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                  designate a different beneficiary. The Spouse may limit his or
                  her consent to a specific form of benefit. (The Spouse's
                  consent is not needed if the Spouse cannot be located or in
                  certain other special circumstances identified in IRS
                  guidance.)

                           (iii) Timing of Waiver. The Participant may waive the
                  QPSA, or revoke the QPSA waiver, at any time; however, if the
                  Participant elects to waive the QPSA, with the consent of his
                  or her Spouse, before the first day of the Plan Year in which
                  the Participant attains age 35, the waiver shall become
                  invalid on the first day of the Plan Year in which the
                  Participant attains age 35.

                           (iv) Explanation. The Committee shall provide the
                  Participant with a written explanation that describes the
                  terms and conditions of the QPSA, the Participant's right to
                  choose another beneficiary, the rights of the Participant's
                  Spouse to insist upon a QPSA, and the Participant's right to
                  revoke his or her election. The written explanation must be
                  provided within the following time limits. If the Participant
                  terminates employment prior to age 35, the explanation must be
                  provided within the period beginning one year before and
                  ending one year after the termination of employment. If the
                  Participant terminates employment on or after age 35, the
                  explanation must be provided within the one of the following
                  periods (whichever period ends last): (i) the period beginning
                  on the first day of the Plan Year in which the Participant
                  attains age 32 and ending on the last day of the Plan Year in
                  which the Participant attains age 34; (ii) the period
                  beginning one year before, and ending one year after, the
                  Participant first becomes eligible to participate in the Plan;
                  and (iii) the period beginning one year before, and ending one
                  year after, a married Participant is fully or partially vested
                  in his or her Account (which will normally occur either when
                  the Participant gets married or when the Participant completes
                  one Year of Service).

5.        Paragraphs 6.3(a)(iii) and 6.3(a)(iv) shall be replaced in their
entirety by the following.

                           (iii) Method of Spouse's Consent. The consent of a
                  Participant's Spouse must be in writing. The consent is not
                  valid unless the Committee has provided the written
                  explanation described in paragraph (iv). The Spouse must
                  acknowledge the affect of his or her consent. The Spouse's
                  consent must be witnessed by a Committee member or by a notary
                  public. The Spouse may limit his or her consent to a specific
                  beneficiary or may allow the Participant to thereafter
                  designate a different beneficiary. The Spouse may limit his or
                  her consent to a specific form of


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                  benefit. (The Spouse's consent is not needed if the Spouse
                  cannot be located or in certain other special circumstances
                  identified in IRS guidance.)

                           (iv) Distribution Procedure.


                                    (A) General. The Committee shall provide the
                           Participant with a written explanation that contains
                           the information required by the Code and Treasury
                           Regulations, as explained in subparagraph (B). The
                           timing of the explanation, the consent, and the
                           distribution are discussed in subparagraph (C). The
                           Participant may revoke his or her election at any
                           time before the distribution is processed.

                                    (B) Contents of Explanation. The information
                           in the explanation shall include, at a minimum, the
                           terms and conditions of the QJSA, the Participant's
                           right to elect a single payment in lieu of a QJSA,
                           the effect of the Participant electing a single
                           payment in lieu of a QJSA, the right of the
                           Participant's Spouse to insist upon a QJSA, and the
                           Participant's right to revoke his or her distribution
                           election.

                                    (C) Timing. The explanation shall be
                           provided no more than 90 days before the annuity
                           starting date. The explanation shall be provided no
                           fewer than 30 days before the annuity starting date,
                           unless all the following conditions are satisfied (1)
                           the Participant affirmatively elects a single sum
                           distribution (and the Participant's Spouse, if any,
                           consents), (2) the explanation mentions that the
                           Participant has a right to at least 30 days to
                           consider whether to waive the QJSA and consent to a
                           single sum, and (3) the Participant is permitted to
                           revoke an affirmative distribution election until the
                           annuity starting date (or, if later, the 8th day
                           after the Participant is provided with the
                           explanation).

                                    (D) Annuity Starting Date. The annuity
                           starting date, for a single sum payment, is the date
                           the payment is processed, which may be any business
                           day. The annuity starting date for a QJSA is the day
                           as of which the annuity payments begin. The annuity
                           starting date for an annuity must be the first day of
                           a month, must occur on or after the Participant's
                           termination of employment or 65th birthday, must
                           occur after the date the explanation is provided, but
                           may precede the date the Participant provides any




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                           affirmative distribution election. In any event, the
                           first payment from the annuity shall not precede the
                           8th day after the explanation is provided.

         6. Section 5.8 shall be replaced in its entirety by the following.

                  A rehired Participant shall have two Accounts, an "old"
         Account for the contributions from his or her earlier episode of
         employment, and a "new" Account for his or her later episode of
         employment. The vested percentage applicable to such Accounts shall be
         determined pursuant to sections 5.1 and 5.6, unless an amount was
         distributed from the old Account before the Participant was rehired, in
         which case the vested percentage of the old Account, after any
         forfeiture has been restored to it, shall be determined pursuant to
         subsection 5.3(c). If a Participant becomes fully vested in both the
         old and the new Accounts, they shall be merged into a single Account.

         7. The last section 10.1 shall be replaced in its entirety by the
following.

                  Apache expects to continue the Plan indefinitely, but the
         continuance of the Plan and the payment of contributions are not
         assumed as contractual obligations. Apache may terminate the Plan or
         discontinue contributions at any time. Upon the termination of the
         Plan, each Participant's Account shall become fully vested. Upon the
         partial termination of the Plan, the Accounts of all affected
         Participants shall become fully vested. The only Participants who are
         affected by a partial termination are those whose employment with the
         Company or Affiliated Entity is terminated as a result of the corporate
         event causing the partial termination; Employees terminated for cause
         and those who leave voluntarily are not affected by a partial
         termination.

                    EXECUTED this 21st day of October, 1999.

                                     APACHE CORPORATION


                                     By: Daniel L. Schaeffer
                                        -------------------------------------
                                     Title: Vice President, Human Resources
                                           ----------------------------------



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