. it has been our practice to issue shares of common stock upon exercise of stock options from previously unissued shares , except in limited circumstances where they are issued from treasury stock . the total number of awards which may be granted in a given year and/or over the life of the plan under each of our equity compensation plans is limited . at december 31 , 2015 , an aggregate of 5.6 million shares were available for future grants and awards under these plans