Spurned by two other prospective merger partners, United Airlines is in serious discussions with US Airways about merging with that airline to create a giant global carrier.

United, the nation's second-biggest carrier, and No. 7 US Airways have been exchanging financial information and discussing terms for weeks, according to three sources familiar with the talks.

No announcement is imminent, and the talks could fall apart. The sources requested anonymity because they aren't authorized to speak publicly.

News reports of the talks sent US Airways shares soaring more than 20 percent yesterday to $8.62. United's parent, UAL, fell 2.6 percent, to $14.81.

The merger under consideration is a stock-swap deal, like the one in which Delta Air Lines proposes to acquire Northwest Airlines.

Together, the airlines operate nine airport hubs — Charlotte, Chicago, Denver, Las Vegas, Los Angeles, Philadelphia, Phoenix, San Francisco and Washington. None of them would be closed initially, the sources said.

United, the leading U.S. carrier to Asia, had courted Delta Air Lines and most recently Continental Airlines, which both have large international networks.

But Delta earlier this month announced a proposed merger with Northwest Airlines instead. Continental's board issued a surprise announcement Sunday breaking off talks with United and saying it wants to remain independent.

United's bid to buy US Airways in 2001 failed when the Justice Department blocked it on the grounds that competition along the East Coast would suffer, especially in the Washington area.