The A's announced the deal Friday and said they optioned Marks to Triple-A Sacramento. Oakland later designated outfielder Kent Matthes for assignment to clear a spot for Marks on the 40-man roster.
The 26-year-old Marks went 3-2 with a 5.64 ERA in 13 appearances with two starts for Triple-A Omaha. He posted a 3.42 ERA with 24 strikeouts in 26 1-3 innings in 11 relief outings.
Marks made his major league debut April 17 against Minnesota after being called up from the minors that day for a brief big league stint.
Matthes was claimed off waivers from Colorado on March 20. He hit .217 with five home runs and 25 RBIs in 48 games with Sacramento and Double-A Midland.