Oswalt is asking the Phillies, or any team that acquires him, to guarantee his $16 million option in 2012 before he would approve a trade, according to two sources familiar with the discussions.
And the Phillies, at least for now, are balking at that request. So unless one side or both changes or softens its stance, Oswalt could be staying put, and the Phillies could be forced to take their hunt for pitching elsewhere.
Oswalt, 32, has about $7 million left on his $15 million salary for this year, plus a guaranteed $16 million next season and either a $2 million buyout or that $16 million option for 2012.
The Phillies are believed to be amenable to paying most of the $25 million he's owed through next year but have shown no inclination to pick up the option year.
It was unclear Wednesday how close the Phillies and Astros were to agreeing on which players would be exchanged if they could resolve Oswalt's contract issues. But there were rumblings from multiple baseball sources that pitcher J.A. Happ would be one of the players heading to Houston in any scenario.
Happ, the runner-up for National League rookie of the year last season, has been pitching in Triple-A, trying to build back strength after an early season forearm injury.
The Astros had scout Doug Brocail on hand Tuesday in Indianapolis to watch Happ throw three hitless innings, striking out three, before being removed early -- ostensibly because the Phillies might need him to replace Jamie Moyer in their rotation this weekend. Moyer left Tuesday's start after one inning because of a left elbow strain.
According to one source who has spoken with both clubs, the rest of the deal likely would be built around prospects who are farther from the majors. The current edition of Baseball America reports that "no team has more talent in A ball than the Phillies." And it's believed the Astros would get one or two players from that prospect pool.
Teams that have spoken with the Phillies say they have rebuffed all attempts to include in any deal their top hitting prospects, Triple-A outfielder Domonic Brown or Class A first baseman Jonathan Singleton. And an elbow injury to their top pitching prospect, Jarred Cosart, apparently has removed him from any current trade talks as well.
So with the Oswalt talks on shaky ground, the Phillies continue to explore other options for upgrading their rotation. They still appear to be pursuing Arizona's Dan Haren and Oakland's Ben Sheets, but they no longer seem to be actively discussing Baltimore's Jeremy Guthrie, Cleveland's Fausto Carmona or Florida's Ricky Nolasco.
Meanwhile, the Phillies still were talking to several teams about outfielder Jayson Werth. But according to an official of one club they spoke with, they've made it clear "they're not going to trade Werth unless they get exactly what they want. They won't do it just to get rid of him."
The Rays still appear to be the front-runners to acquire Werth, if he gets dealt. But one source who spoke with them reports the Phillies asked for pitcher Wade Davis or outfielder B.J. Upton, among others.
And it's difficult to foresee Tampa Bay trading either player just to rent Werth for two months, unless the deal was expanded to send other young, controllable players back to Tampa Bay.
The Red Sox, Yankees and Giants also are believed to have interest in Werth. But there were no signs the Phillies had made much progress in their talks with any of those clubs.
According to an official of one club who spoke with the team, the Phillies aren't willing to pay any of the approximately $3.5 million remaining on Werth's contract.
In fact, one of the Phillies' main motivations in trading Werth, the official said, appears to be "to get rid of all his money."
Jayson Stark is a senior baseball writer for ESPN.com.