This excerpt taken from the HPQ DEF 14A filed Jan 27, 2010.
Issuance of Shares. For purposes of Section 3(a), the aggregate number of Shares issued under the Plan at any time shall equal only the number of Shares actually issued upon exercise or settlement of an Award. If any Shares subject to an Award granted under the Plan are forfeited or such Award is settled in cash or otherwise terminates without the delivery of such Shares, the Shares subject to such Award, to the extent of any such forfeiture, settlement or termination, shall again be available for grant under the Plan. Notwithstanding the foregoing, Shares subject to an Award under the Plan may not again be made available for issuance under the Plan if such Shares are: (i) Shares delivered to or withheld by the Company to pay the exercise price of an Option, (ii) Shares delivered to or withheld by the Company to pay the withholding taxes related to an Award, or (iii) Shares repurchased by the Company on the open market with the proceeds of an Award paid to the Company by or on behalf of the Participant.