The latest unsubstantiated report is that Delta might go after US Airways.
It is also possible that American - which has announced it will cut up to 15,000 jobs, terminate employee pension plans, and reap $2 billion in annual cost savings - will come out of bankruptcy a credible stand-alone company, which is what American wants.
Speculation was further fueled when US Airways chief executive officer Doug Parker told analysts last week that the airline had hired advisers to study a possible bid and that although it did not need a merger, the fifth-largest U.S. carrier was "always interested" in weighing its options.
US Airways has a history of making plays for larger airlines - twice for United Airlines in 2008 and 2010, after which United tied the knot with Continental Airlines Inc., and once in 2007 for then-bankrupt Delta, which merged instead with Northwest Airlines Corp.
"I think people are basically stirring the pot at this point in time," said aviation consultant Robert W. Mann. "I don't have a view as to what's likely, or more likely, or less likely. Just that it will be many months before American presents a reorganization plan and everybody else has a chance to take a shot at it."
As for what would be best for Philadelphia travelers and air service at Philadelphia International Airport, opinions vary.
The surest bet would be for US Airways to go it alone, grow as the economy improves, and retain the more than 400 daily departures in Philadelphia today.
The best growth opportunity for US Airways might be to merge with American - especially if US Airways' management team could end up at the helm.
In this scenario, some think that the combined airline - likely to be called American - would retain the lucrative corporate and local-passenger traffic at New York's JFK Airport, but because of slot constraints that limit American's growth there, shift some European service to Philadelphia.
"A merger with American would probably not change a whole lot in Philadelphia," said airline analyst Helane Becker of Dahlman Rose & Co. L.L.C. "American probably wouldn't mind having some relief to the pressures at JFK. You wouldn't necessarily see a lot of other change because the two airlines don't have a lot of overlapping routes."
A Delta merger would "be more interesting," Becker said. "I would see Delta really not necessarily needing the Philadelphia operation."
Under Delta, Philadelphia might become a "focus" city, but not a big airline hub as it has been. Philadelphia would still have a lot of flights, but maybe not as many frequencies, to as many destinations, and perhaps smaller aircraft on some routes.
Although any deal is months and maybe more than a year away, US Airways could be a better fit to join with American from an antitrust perspective, one analyst said.
"We have serious doubts that regulators would allow either of the two large U.S. legacy carriers, Delta and United, to acquire American," Maxim Group L.L.C. analyst Ray Neidl said in a client note. "We also believe that regulators would have a problem with a Delta acquisition of US Airways due to the extensive overlap in their systems."
On the other hand, a US Airways acquisition of American "could get regulatory approval and the combined airline would have enough market mass to be competitive with Delta and United," Neidl said.
Airline analyst Hunter Keay, of Wolfe Trahan & Co., said Philadelphia could "become less of a focus" if US Airways merged with either American or Delta because both airlines have major operations in New York.
"They would probably utilize Charlotte more as a connecting point for transatlantic traffic if US Airways was to be acquired by anybody," Keay said, referring to US Airways' hub in Charlotte, N.C.
"I think there would be hub redundancies created between JFK and Philadelphia with American and with Delta."
Keay said that no "outcome has a greater than 50 percent probability right now. There are too many other dominoes that could fall."
The most likely scenario is that American will be acquired by TPG Capital, with investment from an airline in the global alliance that includes American, British Airways, Canadian Airlines, Cathay Pacific Airways Ltd., Qantas Airways Ltd., and others, Keay said. (Global alliances help airlines financially because they book travelers on one another's flights. They recognize one another's frequent-flier mileage programs and provide passengers access to airport lounges in other countries.)
Saikat Chaudhuri, a professor at the University of Pennsylvania's Wharton School specializing in mergers and acquisitions, said two scenarios were "most likely" and "strongly favored by American Airlines."
The first is that American stays independent and pulls off an aggressive restructuring.
The second is that American remains independent, but with an investment by British Airways and perhaps TPG. The arrangement would keep intact the Oneworld alliance, to which British Airways and American belong.
"Only if American can't achieve that would they then agree to some kind of merger with these other rivals," said Chaudhuri, an assistant professor of management.
"American would prefer taking over, or merging with, US Airways than being bought by Delta," he said. "I do not think American would agree to be taken over by US Airways." If American sees the benefits of a merger, "they would orchestrate a deal, but on their own terms."
Philadelphia air travel likely will remain as is. "Philly is not threatened, except in the Delta scenario," Chaudhuri said. "Delta probably could taper off the growth."
Said Mann, the aviation consultant: "There is no question that Philadelphia will still have service, no matter what happens here. The question will be who is providing it, how much is there, and to how many continuing destinations."
Contact staff writer Linda Loyd at 215-854-2831 or email@example.com.