The more-experienced options are lefty Boone Logan, who has let all six inherited runners score in his last two outings, and righty John Axford, who seemed to be shaking a slump before losing command in Tuesday night's loss to the Mets.
Miller struggled Monday, giving up three runs in two-thirds of an inning in a loss to the Mets, but he had been pitching well prior to that outing. Oberg has had up-and-down results as a rookie who was in Double-A last year.
"That's part of the plan," Rockies manager Walt Weiss said.