"I feel great, no problems," Oswalt said after throwing approximately 60 pitches in the bullpen Sunday morning.
Oswalt missed his last start due to a strained left oblique muscle, an injury which forced him to leave his previous start on Aug. 18 at San Diego in the fifth inning.
The right-hander warmed up with 15 throws on flat ground and 35 more at a longer distance before moving to the bullpen mound. The strained muscle had been impacting his delivery, particularly when pitching from the stretch, but Oswalt passed both tests Sunday.
"Everything's OK," Oswalt said. "I did both [throw from a full windup and the stretch], everything I needed to do and I feel good, so I'll be ready to go."
Oswalt is 13-6 with a 3.33 ERA in 27 starts.
Sampson getting close: Right-hander Chris Sampson also had a bullpen session Sunday morning and reported no problems.
"It went well," said Sampson, who has been on the disabled list since Aug. 1 because of a right elbow sprain. "I didn't have any discomfort and my control was a little bit better today than when I threw [Friday] night [for Triple-A Round Rock]."
Sampson said he threw between 30-35 pitches. The right-hander is 7-8 with a 4.53 ERA in 20 games, including 19 starts for the Astros, and could be ready to return to the rotation in a week or so.
"Sampson goes on Tuesday for a couple of innings [in a rehab appearance] at Round Rock," Astros manager Phil Garner said.
Rotation plans: With Oswalt back and Sampson and right-hander Brandon Backe [elbow surgery] expected to return in the coming days, Garner will have some decisions to make about the rotation.
September could see six of the seven pitchers who have started for the Astros this season -- Oswalt, Sampson, Woody Williams, Wandy Rodriguez, Matt Albers and Troy Patton -- healthy, with only Jason Jennings (injured and out for the season) out of the picture. Add in Backe and possible September callups like Juan Gutierrez, and Garner will have more starters than rotation spots.
As of Sunday, Garner would only commit to the next series, when Williams, Oswalt and Albers, respectively, will go against the Cardinals.
Patton pitched well in his Major League debut Saturday night and although Garner won't hesitate to use rookies in any situation, he hasn't penciled him in for his next turn, which would be Friday at Chicago.
"He could have not eliminated himself [from consideration to remain in the rotation] yesterday even if he gave up 20 runs," Garner said. "More of a consideration is how he could figure [in the future]. We have to take a look at what we want to do. Looking forward to next year will be a part of the consideration. As long as he's feeling fine and continues to pitch like that, that will be part of his consideration."
Extra bases: The Astros retired first baseman Jeff Bagwell's No. 5 during a pregame ceremony Sunday. He is the ninth player to have his number retired by the club, joining Jim Umbricht (32), Don Wilson (40), Jose Cruz (25), Mike Scott (33), Nolan Ryan (34), Larry Dierker (49), Jimmy Wynn (24) and the No. 42 retired by all of Major League Baseball in honor of Jackie Robinson. The Astros had special first bases installed for Sunday's game with the words Jeff Bagwell Jersey Retirement Day imprinted on them. Bagwell will be given one of the bases and the rest will be auctioned off with proceeds to benefit charity. ... Craig Biggio was not in the lineup Sunday as Chris Burke started at second base. Biggio has 3,040 career hits and needs 13 to tie Rod Carew for 21st place on the all-time list.
On deck: The Astros are off Monday and will begin a three-game series against St. Louis on Tuesday at Minute Maid Park. Woody Williams (8-12, 4.84 ERA) will get the start for the Astros against right-hander Braden Looper (10-10, 4.90). First pitch is 7:05 p.m. CT.
Jim Molony is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.