This excerpt taken from the DVN DEF 14A filed Apr 28, 2008.
Restricted stock awards are grants of our common stock that will only be earned by an executive officer when the restrictions lapse and only if the individual continues to be employed by us at that time. During the vesting period, the forfeitable value of a restricted stock award is less volatile than the forfeitable value of a stock option award with same economic value at grant. A more constant forfeitable value makes restricted shares an effective tool for attracting and retaining top executive talent in a competitive industry. For awards made in 2007, one quarter of each award vests on each of the first four anniversary dates of the original grant. As with stock options, the vesting schedule provides incentive to continue service with the Company for an extended period.