EXHIBIT 10.21










                                  April 8, 2005


Mr. Mark S. Berg

     Re:  Offer of Employment

Dear Mark:

     It is my pleasure to memorialize the terms of our offer for the position of
EVP,  General  Counsel and Secretary in the Legal  Department at Pioneer Natural
Resources USA, Inc.

     This  position  will  report to Scott  Sheffield,  Chairman  & CEO and will
include an initial  base salary of  $27,500.00  per month and an initial  annual
target bonus of 65 percent  based on your  individual  performance,  the Company
meeting  prescribed  goals  annually  and  approval  by the  Company's  Board of
Directors. In addition, you will be eligible for restricted shares equivalent to
a value of $550,000.  The bonus and restricted  stock award will be based upon a
full year and will not be prorated.  You will receive 4 weeks vacation annually.
The  attached  "Compensation/Benefits  Package"  covers  the  features  of these
programs in more detail and is considered a part of our employment offer.

     As a regular  employee of Pioneer Natural  Resources,  you will be eligible
for  participation  in the Company's group insurance and other employee  benefit
programs. As stated in the Company's Employee Handbook, the Company reserves the
right to amend,  modify, or discontinue specific employee benefits and personnel
policies  at any time,  and your  rights and  benefits  will be  governed by the
policies as they exist from time to time.

     In accepting this offer of employment, you will be accepting responsibility
for  protecting  information  proprietary to Pioneer  Natural  Resources and its
affiliated  entities  and  to  use  such  information  exclusively  for  Company
purposes,  and during your  employment,  you agree to forego any and all gainful
employment which would in any way adversely  impinge upon the business  interest
of Pioneer Natural Resources or your ability to perform your job.

     Your  acceptance  of  this  offer  places  you  in  the  Company's  regular
employment  status with the presumption  that you will remain a Pioneer employee
for an indefinite period. It must, however, be understood that you will be on an
"employment  at will"  status,  meaning that your  employment  by Pioneer may be
terminated  at any time by either you or the Company for no reason or any reason
not prohibited by law.











Offer of Employment                                               April 8, 2005
Page 2


     Please execute in the space below to indicate your agreement and acceptance
of the terms of the offer outlined in this letter.

                                                     Sincerely,


                                                       /s/ Scott D. Sheffield
                                                     -------------------------
                                                     Scott Sheffield
                                                     Chairman & CEO


Accepted:

   /s/ Mark S. Berg
- ------------------------------
Mr. Mark S. Berg













                          COMPENSATION/BENEFITS PACKAGE
                                Mr. Mark S. Berg

Title:                       EVP, General Counsel and Secretary

Base Salary:                 $330,000 per year

Annual Bonus:                Initial target bonus of 65 percent of base salary.

Long-term Incentive:         Eligible for  Annual  Restricted  Stock  subject to
                             Board approval,  individual  performance and  share
                             availability.  Your  Executive  Officer position is
                             currently  eligible for  Restricted  Stock  with a
                             value of  approximately $550,000  and subject  to 3
                             year cliff vesting period.  You will receive a full
                             annual award for 2005 of 16,000 shares.

Retirement Plan:             401(k) Plan - Employee may  defer up to 30% pre-tax
                             and up to 20% post-tax.  Company match is $2 for $1
                             - up to 5% of base salary.

Non-Qualified Deferred
Compensation Plan:           Retirement  plan  on  a   pre-tax  basis   allowing
                             deferral of up  to 25 percent  of annual salary and
                             100% of  bonus each  year.  The Company  provides a
                             matching contribution of up to 10% of base salary.

Club Membership:             Eligible for fees  related to initiation,  dues and
                             membership.

Vacation:                    4 weeks annually

Health Insurance:            Medical/Dental/Prescription  coverage  -   Employee
                             pays $22 per  month for  employee coverage  and the
                             employee pays portion of dependent cost.

Life Insurance:              Company pays for 2x base  salary life insurance and
                             2x   base  salary  AD&D  insurance.   Company  also
                             provides business travel life insurance.

Long Term Disability:        Company pays premium for disability insurance that
                             provides 60% income replacement.

Holidays:                    Nine  (9)  scheduled  holidays  plus  one  floating
                             holiday.

Additional Company Paid
Benefits:                    Short-term   Disability,   Sick   Leave,    Tuition
                             Reimbursement

Relocation Package:          Per Company  policy (existing employee policy). You
                             will  not  be   required  to  reimburse  relocation
                             benefits  under   the   policy  as  a   result   of
                             termination  of your  employment where you would be
                             entitled to severance payments from the Company.









Change In Control and
Severance Agreement:         2.99 X base  salary and  bonus in  the event of CIC
                             followed  by  termination  within one  year of CIC.
                             Form of  agreement  is being  reviewed by Board for
                             approval, but you will be entitled to the same form
                             of CIC and severance  agreement as other  similarly
                             situated   executive   officers   serving  on   the
                             Management Committee.