This excerpt taken from the BP 20-F filed Mar 6, 2007.
BP ShareSave Plan
A savings-related share option plan, under which employees save on a monthly basis over a three-or five-year period towards the purchase of shares at fixed price determined when the option is granted. This price is usually set at a 20% discount to the market price at the time of grant. The option must be exercised within six months of maturity of the savings contract; otherwise it lapses. The plan is run in the UK and options are granted annually, usually in June. Until 2003, a three-year savings plan was also run in a small number of other countries. Options will remain outstanding in respect of these countries until the end of June 2007. Participants leaving for a qualifying reason will have six months in which to use their savings to exercise their options on a pro-rated basis.