"I feel great," Oswalt said in a conference call Wednesday. "I feel as good as I've always felt. I don't really have any complications anywhere right now. The biggest thing is to get back going and get a few starts under your belt where you have muscle memory and feel comfortable. You can start building off that."
Scott Feldman, who won his first game of the season Tuesday, will return to the bullpen. Justin Grimm, the Double-A pitcher who made a successful big league debut Saturday, will stay in the rotation for now and pitch Monday against the Detroit Tigers.
Oswalt, 34, signed with the Rangers last month and has made four starts in the minor leagues to build arm strength. The right-hander's latest start was a sign that he was ready to join the Texas rotation as he gave up two runs on six hits with a walk and five strikeouts, helping Triple-A Round Rock to a 4-2 win against Oklahoma City on Sunday.
"He brings experience, pitched in many big-time games," Rangers manager Ron Washington said Wednesday. "We know he's not intimidated. We certainly expect him to eat a lot of innings and by eating those innings, help us win ballgames. That's the bottom line: helping us win ballgames.
"His last start proved he's ready to pitch."
Before that outing, Oswalt had a 7.71 ERA in 9 1/3 innings in one start with Double-A Frisco and two with Round Rock.
But on Sunday, he threw 100 pitches and impressed club officials. Among those watching was Rangers CEO Nolan Ryan, who came away "comfortable" with Oswalt making his next start in a Rangers uniform.
"I thought he pitched to both sides of the plate (Sunday) night and maintained his stuff throughout the game," Ryan said Monday on ESPN Dallas 103.3 FM's "Galloway and Company."
"There wasn't a wow factor to his game, but the ball was coming out of his hand well," Ryan said. "I thought he went about his business the way I would expect him to. He was making pitches and doing things I anticipated seeing him do."
Oswalt feels he's ready to help the Rangers rotation.
"I think I'm pretty close," Oswalt said. "The biggest thing down here was to build some arm strength and get back into pitching shape. You can throw a lot of bullpens and lift a lot of weights, but until you get out there and compete against hitters and get into pitching shape, you can't duplicate it."
Friday will be Oswalt's first start since he lost Game 4 of the 2011 National League Division Series to the St. Louis Cardinals while a member of the Philadelphia Phillies. His last regular-season outing was six shutout innings in a win against the Atlanta Braves on Sept. 27, 2011.
"That's what you play for is to get back out here," Oswalt said. "Everyone that plays this game is looking for competition. You miss that when you're not around it, and I'm looking forward to it. I've been watching this team for the last two years and thought I'd be competing against them (in the playoffs. The Phillies) thought we had the best team in the NL and fell short. It's just a solid team, and I'm ready to get back on the field."
Oswalt is 8-2 with a 1.92 ERA in 12 career starts against the Rockies.
He has a 159-93 record and a 3.21 ERA mark in 339 career games with the Houston Astros and Philadelphia.
Feldman is 1-6 with a 6.00 ERA this season. He has made 13 appearances, including eight starts.
"There's a need in the bullpen," Washington said. "Grimm threw the ball well, and he certainly deserved another shot. We weren't going to throw him in the bullpen."