Dr. James Andrews performed the procedure, often called Tommy John surgery. Outman went 4-1 with a 3.48 ERA this season in 14 appearances, including 12 starts. Outman also had a bone spur removed.
The surgery typically requires a year or more of rehabilitation. Prospective A's closer Joey Devine underwent the same procedure in April, and Oakland reliever Dan Giese also underwent elbow surgery earlier this season.
A's right-hander Justin Duchscherer, a two-time All-Star, resumed a throwing program Tuesday after undergoing elbow surgery in March.