This excerpt taken from the BP 20-F filed Jun 30, 2005.
Transfer of Shares on Exercise of Awards
8.1 Subject to any necessary consents, to payment being made for the Shares and to compliance by the Participant with the terms of the Plan, not later than 30 days after vesting (or, if applicable, receipt of valid notice of exercise), the Company shall procure the transfer of Shares to the Participant (or to his nominee). The Company shall (unless the Shares are to be issued in uncertificated form) as soon as practicable deliver to the Participant (or his nominee) a definitive share certificate or other evidence of title in respect of such Shares.
8.2 The Company shall not be obligated to procure the transfer of Shares in connection with any Award or take any other action under the Plan in a transaction subject to the requirements of any applicable securities law, any requirement under any listing agreement between the Company and any securities exchange or automated quotation system or any other law, regulation or contractual obligation of the company until the Company is satisfied that such laws, regulations, and other obligations of the Company have been complied with in full. The Company may require any Participant to make such representations and furnish such information as it may consider appropriate in connection with the transfer of Shares under the Plan. Certificates representing Shares will be subject to such stop-transfer orders and other restrictions as may be applicable under such laws, regulations and other obligations of the Company, and a legend or legends may be placed thereon to reflect such restrictions.