The players will compete for a total purse of $1 million using the Skins format in which a golfer must win the hole outright to collect the kitty. If two or more golfers tie, the money carries over to the next hole.
Ames won last year's Skins Game with a birdie on the last hole that was worth $650,000. He won the 2006 event on the second playoff hole, which was worth $270,000, giving him a total take of $590,000.
Mickelson, the No. 2-rated player in the world, last played in the Skins Games in 2003, when he finished third with $170,000. He was second in 2002.
Choi and Mediate, who had a thrilling head-to-head battle with Tiger Woods for the U.S. Open title this year, haven't appeared in the Skins Game before.