This excerpt taken from the DVN DEF 14A filed Apr 27, 2007.
Defined Benefit Plan
The Defined Benefit Plan is a qualified defined benefit retirement plan which provides benefits based upon employment service with us. All of our employees become eligible to participate in the Defined Benefit Plan when they earn one year of service and attain the age of 21 years. Each eligible employee who retires is entitled to receive monthly retirement income, based upon their final average compensation and credited years of service. Contributions by employees are neither required nor permitted under the Defined Benefit Plan. Benefits are computed based on straight-life annuity amounts and are reduced by Social Security benefits payable to the employee. Benefits under the Defined Benefit Plan are reduced for certain highly compensated employees, including our named executive officers, in order to comply with certain requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA) and the Code.