FWAAA

Of course there's a possibility that US could switch from Star Alliance to Oneworld before a merger or if the merger is blocked.

Is it likely? I don't believe it is.

Here's why: Parker has said that Star Alliance has been good for US. If he wanted US in Oneworld, then why did US join Star in 2004? And why hasn't US joined Oneworld in the intervening years?

Answer: Either Parker values being in Star more than being in Oneworld or because Oneworld turned him down sometime in the previous 12 years since he took over as US CEO.

We don't know the answers.

One thing we do know is that Parker engineered a hostile takeover of AA last February. We know that Horton was not in favor of the merger, but that AA creditors were sold on the merger and overruled Horton.

Another almost indisputable fact is that there was no chance that a combined US-AA would be permitted to join Star, especially not the immunized alliances that AA has with BA/IB and JAL. European regulators have hinted that they aren't happy that many of the world's airlines have paired off into just three big alliances. No way would they approve the world's two largest airlines (AA and UA) to be in the same antitrust immunized alliance. Not a chance at all.

My guess (gut feeling - no evidence) is that US was planning to join Oneworld solely because that was the only possible result following the merger with AA. IMO, if there is no merger, then there is no push by US to join Oneworld and there is no push by other Oneworld members (not even AA) to invite US to join.

Bottom line: US joins OW if the merger happens, and stays where it is if the merger does not happen.