The A's agreed to terms with their second-round Draft pick, Dillon Overton, on Wednesday.
With the addition of the left-hander, Oakland has signed each of its first 15 picks and 32 of its 42 overall from the 2013 First-Year Player Draft.
Overton, who played at Oklahoma, went 9-3 with a 3.02 ERA in 16 games this season -- 14 of them starts. He posted a career 2.89 ERA as a Sooner.
In this year's NCAA tournament, Overton went 0-1, allowing five earned runs in 11 2/3 innings over two starts. He was solid in a regional contest against UConn but picked up the loss in a Super Regional elimination game against LSU.