This excerpt taken from the BP 20-F filed Jun 30, 2005.
Specific Provisions relating to the Share Element
4.1 The Committee may, at its absolute discretion, grant the Share Element during any Grant Period. The Share Element will normally be subject to a demanding performance condition. The performance condition attaching to Awards under this Element will be determined by the Committee at the time of grant and will usually require a sustained improvement in the Company's performance, normally relative to its peer group, over a Performance Period.
4.2 The Shares awarded on maturity of this Element will normally be subject to a compulsory retention period determined by the Committee which will not normally be less than three years. Shares will only be released at the end of the retention period if the Company's minimum shareholding guidelines (as determined by the Committee from time to time) have been met.
4.3 The Grant Letter issued under rule 2.4 shall specify, inter alia, the following:
4.4 In exceptional circumstances, the Committee may make Awards under the Share Element which are subject to a requirement of continued service over a specified period, rather than a corporate performance condition. Such Awards will only be made as an element in a recruitment or retention incentive or as a reward for exceptional achievement of projects.