DENVER -- At the age of 35, and financially set for life, Roy Oswalt still has the competitive drive that won't allow him to just walk away from the game.

So instead of hanging around the house, he finds himself in Tulsa, Okla., pitching for the Rockies' Double-A Tulsa affiliate, getting ready to make a fifth start on Friday night that will set the stage for his return to the big leagues next week as a member of the Rockies' rotation.

Oswalt tried this midseason arrival with Texas last year, but it wasn't a good fit.

He didn't perform at the level needed to satisfy himself or the Rangers, who were headed to the postseason for the third year in a row. With a 3-3 record and 6.36 ERA in nine starts, he finished the year in the bullpen, and disappointed.

The desire to play baseball, however, did not die. It still ate at him during the spring, when others were getting ready for the season, and it sent him in search of another chance, which the Rockies provided.

"The biggest thing is the passion for the game," Oswalt said in an interview with ROOT Sports Rocky Mountain. "You go home and think about what you've done for 20 years, and you kind of watch it from the sideline, and you know you can still do it.

"I think that was the hardest part to get over. Seeing the guys play and watching baseball on TV made it even worse. I think the passion for the game kind of got to me, and I knew I had a good many years I could probably still play, and I want to do it until I can't do it [any] more. ... I thought it would be a good time to go back last year, went back and kind of got behind the eight ball early, and this year kind of dedicated myself to it, and got in better shape and should be ready to go."

Oswalt and the Rockies are a good fit.

The Rockies have surprised more than a few with their strong play this season. They went into Wednesday night just a game back of first-place Arizona in the National League West, and a game ahead of the defending world champion San Francisco Giants.

But they also know that to stay in contention for the postseason, they need to upgrade the rotation. They have a solid starting trio with Jorge De La Rosa, Jhoulys Chacin and Tyler Chatwood, but then ...

Jeff Francis is the consummate pro, but he has worked only 40 innings in nine starts and has managed to get through six innings -- but not a pitch more -- only twice. He starts on Thursday in what could be a deciding factor of his future.

Juan Nicasio still has the power arm and competitive fire but is missing the command that made him special before he was hit in the forehead with a line drive and suffered a fractured neck two years ago. And he has not mastered the secondary pitches to allow him to pitch deep into a game.

He is averaging 17.4 pitches an inning, second in the NL behind Lucas Harrell of Houston, who averages 18.1. As a result, Nicasio averages barely more than five innings a start and has yet to exceed six innings.

Enter Oswalt, who is 2-2 with a 2.88 ERA in his first four starts at Tulsa. He has walked only six batters in 25 innings. He has worked seven innings in his last two outings, throwing 95 pitches in his previous start and is expected to throw 105 or even a few more on Friday.

Oswalt has an opt-out clause in his contract next week if he is not in the big leagues.

That, however, is not likely going to be a factor.

"We set a plan before I even signed," Oswalt said. "Bill [Geivett, senior director Major League operations] and I sat down together and got a plan together. He didn't want to rush me. He felt that last year the Rangers rushed me a little bit getting me up, and I think a lot of it was due to a lot of injuries on the starting staff and they needed an arm, and I felt like I was ready to go. This year, I think we have a better plan, and I feel like I'm a lot more ahead of the game then I was last year."

Oswalt, who has earned $96 million in 12 big league seasons, knows about success. He reached double figures in wins in nine of his first 10 full seasons. He has a 163-96 big league record.

He pitched in the postseason with Houston in 2004 and '05, and with Philadelphia in 2010 and '11. He'd like to add a fifth postseason to his resume in 2013 with Colorado, returning to an NL team after his first AL exposure a year ago.

"I have been a National League guy all my life," he said. "I like the style of baseball, the hit and running, double switching, a little bit more thought process goes into it from a managing standpoint."

And he's ready to give the Rockies something else to think about in their rotation.