"There is definite interest globally in Philadelphia," airport chief of staff Jeff Shull said this week.
But with Southwest planning to start service here in May, some of the other low-fare airlines probably will stay away, airline-industry consultants said.
"I don't think there's room for everybody," said Mo Garfinkel, head of GCW Consulting in Arlington, Va.
Even as Southwest was looking at Philadelphia last spring and summer, officials from the other three airlines were making inspection trips here, Shull and others said.
Frontier Airlines, which is based in Denver and which flies to both coasts and to Mexico, has sent officials to Philadelphia "a few times" during the last year, spokesman Joe Hodas said. "It's definitely on a list of about a dozen cities" where Frontier could expand in the next several years, he said.
Virgin USA, which has said it plans to start its low-fare operation by next summer, has looked both at locating its corporate headquarters in Philadelphia and at flying from the airport, Virgin Group and city officials said.
Virgin Group spokesman Todd Pawlowski said Virgin USA would select its headquarters city by the end of the year. Branson, who controls Virgin Atlantic Airways and low-fare airlines in Europe and Australia, would be a minority shareholder of Virgin USA because of federal laws prohibiting non-U.S. citizens from controlling U.S. airlines, Pawlowski said.
JetBlue spokeswoman Fiona Morrisson said her company, which is based in New York's Kennedy International Airport, had "been to a lot of cities," including Philadelphia, to check out facilities, but had no plans to start service here.
Southwest, the world's largest discount airline, announced Oct. 28 that it would start service to Philadelphia with 14 flights a day, using four gates in Terminal E. Southwest plans to announce by mid-December the handful of cities it will serve when it starts. Company officials have said that the airline expects to steadily add flights to other places over the next few years.
Philadelphia air travel now is dominated by US Airways, which carries almost 60 percent of the airport's passengers and has nonstop service to more than 125 U.S. and foreign cities. Two smaller low-fare carriers, Air Tran Airways and ATA Airlines, have flights on seven routes. But US Airways and other major airlines have the only service to most cities, which keeps fares higher than they are on the routes where AirTran and ATA compete.
Airline experts say they are not surprised by the interest in Philadelphia by other carriers, given the region's large population and base of business travelers. But Southwest's move to come here may have preempted the other carriers' plans, they said.
"There's clearly room for Frontier, because they fly from Denver and Southwest doesn't serve Denver," Garfinkel, the head of GCW Consulting, said. "But I think Virgin USA will take [Philadelphia] off its list because Southwest is there."
Contact staff writer Tom Belden at 215-854-2454 or email@example.com.