Oswalt had been sidelined by a strained left hamstring. The veteran right-hander signed a minor league deal with Colorado in May and is 0-4 with a 7.64 ERA in four starts with the Rockies.
Pomeranz had been out with left biceps tendinitis. The lefty is 0-4 with an 8.10 ERA in four starts.
The Rockies made the moves before Friday night's game against San Diego.