This excerpt taken from the SIRI DEF 14A filed Apr 30, 2009.
No Liberal Recycling Provisions
The Plan provides that only shares covering awards that expire or are forfeited or cancelled, or shares that were covered by an award the benefit of which is paid in cash instead of shares, will again be available for issuance under the Plan. The following shares will not be added back to the aggregate Plan limit: (i) shares tendered in payment of the option price; and (ii) shares withheld by us to satisfy the tax withholding obligation. Further, all shares covered by a SAR, to the extent that it is exercised and settled in shares, and whether or not shares are actually issued to the participant upon exercise of the right, will be considered issued or transferred pursuant to the Plan.