This excerpt taken from the CVS DEF 14A filed Apr 4, 2007.
11. Interest. No interest shall accrue on the payroll deductions of a participant in the Plan
(a) The maximum number of shares of Stock which shall be made available for sale under the Plan shall be fifteen (15) million shares, subject to adjustment as provided in Section 18 hereof. If, on a given Exercise Date, the number of shares with respect to which options are to be exercised exceeds the number of shares then available under the Plan, the Company shall make a pro rata allocation of the shares remaining available for purchase in as uniform a manner as shall be practicable and as it shall determine to be equitable. Any shares of Stock delivered by the Company under the Plan may consist, in whole or in part, of authorized and unissued shares or shares acquired by the Company in the open market. Shares acquired in the open market through dividend reinvestment will not count against the Reserves.
(b) The participant shall have no interest or voting right in shares purchasable upon exercise of his or her option until such option has been exercised.