Washington said it all comes down to Feliz's stuff over the other candidates.
"We'll just see how he'll handle it," Washington said. "If he can locate his fastball, there's no doubt he can get us those three outs."
The Rangers decided in Spring Training that Feliz is better suited for the bullpen. He is still working on developing his curve and changeup, but his best pitch is a fastball that can register over 100 mph on the radar gun.
"We talked to him a lot when he was a starter about using all his pitches," Washington said. "Now, as a reliever, he's in an attack mode -- use his best stuff and leave it out there. He can still use his secondary stuff, but he realizes his fastball is his best weapon.
"If you command the fastball, you don't have to be outstanding with your secondary stuff. You just have to be able to get it across. If they're sitting on the hard stuff, you can lock them up if you can get your secondary stuff over the plate."
Feliz, 21, spent the final two months of last season with the Rangers and was 1-0 with a 1.74 ERA in 20 appearances while striking out 39 batters in 31 innings. He walked eight and allowed 13 hits.
Feliz had the second-lowest ERA of any American League reliever with at least 30 innings last year. His .124 opponents' batting average was the lowest and he was eighth with 11.32 strikeouts per nine innings.
"I feel good about it," Feliz said. "They put me in the bullpen, now I can just come in there and fire it up there. I'm ready to go, I just want to be healthy and pitch."
Washington said he wants to limit Feliz to one inning per outing.
"Our plan is to use him for one inning, and with the weapons we have down there, we should be able to use him for one inning," Washington said.
Oliver will likely pitch anywhere between the sixth and eighth innings and is the Rangers best option against a tough left-handed hitter late in the game. But Washington said Oliver will not be limited to left-handed hitters and he will not necessarily be limited to just one inning.
"He could come in, get the last out of an inning and then come back for another inning," Washington said. "
Oliver is the only left-hander in the Rangers' bullpen. Chris Ray, with his split-fingered fastball, is the Rangers' second-best relief option if they need somebody to get a left-handed hitter before the eighth inning. When he saved 33 games for the Orioles in 2006, he held left-handed hitters to a .193 batting average.
Darren O'Day, a side-arming right-hander, is tough on right-handed hitters, holding them to a .180 batting average last season. But left-handed hitters batted just .239 off him, which isn't bad, either.
As with Feliz, both O'Day and Ray will likely be limited to one inning of work per outing. The Rangers have both Doug Mathis and Dustin Nippert to give them multiple innings as middle or long relievers.