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.