What that means for Neftali Feliz once he returns from the disabled list remains to be seen, but it is a move that no doubt makes the Rangers a deeper, better team moving forward.
With Oswalt in the fold, here is a look at where the Rangers rank among the 10 best rotations in all of baseball.
1. Erik Bedard (3-5, 3.12 ERA, 51 Ks, 52 IP)
2. James McDonald (4-2, 2.20 ERA, 63 Ks, 65.1 IP)
3. A.J. Burnett (3-2, 4.19 ERA, 39 Ks, 43 IP)
4. Charlie Morton (2-6, 4.65 ERA, 25 Ks, 50.1 IP)
5. Kevin Correia (1-5, 4.30 ERA, 18 Ks, 52.1 IP)
After watching their unproven starting staff crumble down the stretch last season, the Pirates added a pair of veterans this offseason in Bedard and Burnett—and both pitchers are enjoying bounce-back seasons.
The true stud of the staff, though, is McDonald, who has taken the next step as a 27-year-old and is currently one of the most underrated and overlooked pitchers in all of baseball.
Morton and Correia are passable starters at this point. So is Jeff Karstens who is currently on the disabled list, and as long as those guys continue to eat innings and posted sub-5.00 ERA they are doing their jobs.
1. Justin Verlander (5-3, 2.55 ERA, 82 Ks, 81.1 IP)
2. Doug Fister (0-3, 3.15 ERA, 24 Ks, 34.1 IP)
3. Drew Smyly (2-1, 3.14 ERA, 46 Ks, 48.2 IP)
4. Max Scherzer (4-3, 5.67 ERA, 72 Ks, 54 IP)
5. Rick Porcello (3-4, 5.21 ERA, 35 Ks, 57 IP
Anchored by the AL's best pitcher in Verlander, the Tigers staff cracks the list despite having a pair of starters with ERAs north of 5.00.
However, the always streaky Scherzer has been better of late with a 3.65 ERA and 24 strikeouts in 12.1 innings of work over his last two starts. Porcello, meanwhile, has five quality starts in 10 outings this year so it hasn't been all bad.
The real X-factor here has been Smyly, who won the fifth starter job over top prospect Jacob Turner and has given the Tigers a reliable second starter in the absence of Fister, who recently returned from injury.
1. Josh Johnson (2-3, 4.87 ERA, 45 Ks, 57.1 IP)
2. Mark Buehrle (5-4, 3.26 ERA, 34 Ks, 69 IP)
3. Ricky Nolasco (5-3, 4.26 ERA, 34 Ks, 61.1 IP)
4. Carlos Zambrano (3-3, 3.00 ERA, 49 Ks, 66 IP)
5. Anibal Sanchez (3-3, 2.57 ERA, 67 Ks, 66.2 IP)
After a troublingly slow start to the season, the Marlins have begun to turn things around, and their pitching has been a big reason why.
Acquisitions Buehrle and Zambrano have been as good and better than expected, respectively. They have helped fill out the staff and give the Marlins as deep a rotation 1-5 as any team in baseball.
Johnson has bounced back from a horrible start, as he has a 2.77 ERA in 26 innings over his last four starts and once again looks like the ace of the staff.
Sanchez is in a contract year, and with his health problems appearing to be a thing of the past he could be in line for a big payday.
1. Jered Weaver (6-1, 2.61 ERA, 57 Ks, 69 IP)*
2. Dan Haren (3-5, 3.52 ERA, 66 Ks, 71.2 IP)
3. C.J. Wilson (6-4, 2.77 ERA, 59 Ks, 65 IP)
4. Ervin Santana (2-6, 4.45 ERA, 48 Ks, 64.2 IP)
5. Jerome Williams (5-2, 3.81 ERA, 38 Ks, 59 IP)
Santana has rebounded nicely after posting a 7.23 ERA through his first four starts, as he has a 2.85 ERA and five quality starts in his last six outings.
Rounding things out, Williams continues to be one of the better scrap-heap findings in recent memory as he has a 9-2 record and 3.76 ERA since joining the Angels last season. That, after not pitching in the majors since 2007.
*Note: Jered Weaver has been placed on the 15-day DL with a lower back injury; Garrett Richards will take his spot in the rotation. This obviously knocks the Angels down the rankings for now, and out of these rankings altogether if the injury is serious enough that he misses more time than that.
1. Colby Lewis (4-3, 3.58 ERA, 59 Ks, 65.1 IP)
2. Derek Holland (4-3, 4.05 ERA, 55 Ks, 60 IP)
3. Yu Darvish (7-2, 3.25 ERA, 66 Ks, 61 IP)
4. Matt Harrison (6-3, 4.41 ERA, 41 Ks, 63.1 IP)
5. Roy Oswalt
Oswalt will report to Triple-A Round Rock, but he has reportedly been throwing regularly so it likely won't take him long to round into form.
Scott Feldman will hold down his rotation spot for now, as he has moved into the rotation with Neftali Feliz on the shelf with arm soreness. Once he returns, the team will have to decide between sending Feliz or Harrison to the bullpen, with Feliz being the more likely candidate.
Darvish has proven to be worth the exorbitant amount the Rangers paid for him, while Lewis and Holland continue to serve as solid innings eaters with proven postseason track records.
1. Tim Lincecum (2-5, 6.41 ERA, 58 Ks, 53.1 IP)
2. Matt Cain (5-2, 2.79 ERA, 66 Ks, 71 IP)
3. Madison Bumgarner (5-4, 3.14 ERA, 47 Ks, 66 IP)
4. Barry Zito (4-2, 3.41 ERA, 34 Ks, 58 IP)
5. Ryan Vogelsong (3-2, 2.36 ERA, 46 Ks, 61 IP)
Even with ace Tim Lincecum struggling like never before, the Giants earn a spot in these rankings as none of their other four starters has an ERA over 3.50.
Cain earned a massive extension in the offseason, and he has shown why he was worth every penny so far. Zito is enjoying a bounce-back season, while Vogelsong has proven that last year's out-of-nowhere All-Star campaign was no fluke.
It will be interesting to see just how good Bumgarner is in his prime, as he already has 62 starts under his belt at the age o 22. He's done better than anyone could have expected in those starts with a 25-23 record and 3.10 ERA.
1. Clayton Kershaw (4-2, 1.97 ERA, 57 Ks, 68.2 IP)
2. Chad Billingsley (2-3, 3.88 ERA, 52 Ks, 55.2 IP)
3. Chris Capuano (7-1, 2.14 ERA, 58 Ks, 63 IP)
4. Aaron Harang (3-3, 4.14 ERA, 50 Ks, 58.2 IP)
5. Nathan Eovaldi (0-1, 2.57 ERA, 4 Ks, 7 IP)
The Dodgers have the best record in baseball thanks in large part to their starting pitching, once again fronted by one of the game's top young stars in Clayton Kershaw.
The biggest surprise has been Capuano though, as he was signed to a two-year, $10 million deal this offseason to fill out the back end of the rotation and has pitched like a staff ace.
The team was dealt a blow when Ted Lilly (5-1, 3.14 ERA) was shelved with shoulder inflammation that could sideline him for an extended period of time, but Eovaldi proved more than capable as a rookie last season.
1. Kyle Lohse (5-1, 2.90 ERA, 36 Ks, 62 IP)
2. Jaime Garcia (3-3, 3.78 ERA, 49 Ks, 64.1 IP)
3. Adam Wainwright (4-5, 4.45 ERA, 51 Ks, 58.2 IP)
4. Lance Lynn (8-1, 2.54 ERA, 60 Ks, 63.2 IP)
5. Jake Westbrook (4-4, 3.69 ERA, 44 Ks, 61 IP)
If you would have told me before the season started that Chris Carpenter would not be pitching and Adam Wainwright would be slow to come back from injury, I never would have guessed the Cardinals would be doing as well as they have.
However, Lohse has stepped up in the role of staff ace and Lynn has been nothing short of phenomenal as Carpenter's replacement.
Also, Wainwright is starting to hit his stride with a 0.60 ERA over his last two starts, including a four-hit shutout of the Padres.
1. James Shields (6-3, 3.95 ERA, 74 Ks, 73 IP)
2. David Price (6-3, 2.71 ERA, 57 Ks, 66.1 IP)
3. Jeremy Hellickson (4-1, 2.83 ERA, 41 Ks, 63.2 IP)
4. Matt Moore (1-5, 4.76 ERA, 58 Ks, 56.2 IP)
5. Alex Cobb (2-0, 2.25 ERA, 8 Ks, 12 IP)
The Rays continue to reap the rewards of good drafting and player development with an entirely homegrown rotation.
Rookie Matt Moore has been the weak link of the group so far, but he may have turned a corner in his last outing when he struck out 10 and allowed just four hits in seven innings, although he wound up taking the loss.
Cobb has filled in nicely for injured Jeff Niemann, and is just an example of the type of quality depth the Rays have at the position outside of their starting five.
1. Stephen Strasburg (5-1, 2.64 ERA, 70 Ks, 58 IP)
2. Gio Gonzalez (7-1, 2.04 ERA, 79 Ks, 61.2 IP)
3. Jordan Zimmerman (3-5, 2.80 ERA, 44 Ks, 64.1 IP)
4. Edwin Jackson (1-3, 3.17 ERA, 53 Ks, 65.1 IP)
5. Chien-Ming Wang (1-0, 3.00 ERA, 0 Ks, 3 IP)
The Nationals have been one of the biggest surprises of the 2012 season, and it is due in large part to their fantastic pitching staff.
They have a 2.96 team ERA, which is tops in all of baseball. Gio Gonzalez may be the best pitcher in the National League right now as he has proven more than worth the package of four prospects the Nationals gave up to get him from the A's.
Wang's return from injury displaces Ross Detwiler (3-3, 3.88 ERA, 36 Ks, 48.2 IP), who by all accounts is having a season that would make him the best pitcher on a number of other teams.