"In normal times, this number of carriers is able to make money," Bailey said. "Things were looking pretty good for the last two or three years."

With the Bush administration's deal-friendly Justice Department in charge until January 20, 2009, hardly an antitrust concern has been raised in the past month of merger mania in the airline industry.

Delta's agreement to buy Northwest has set the airlines scrambling like desperate singles at a square dance. Money-losing United is especially in the grip of merger fever. "Consolidation is underway; ensuring you have the right partner is everything," United Airlines chief executive Glenn Tilton said over the weekend.

Borenstein said airline C.E.O.'s have a window of opportunity to get a deal done, and they are desperate to act before it closes.

"They see the end of the Bush administration coming and an almost certain increase in antitrust scrutiny of airline mergers after January 20," he said. "So they feel real time pressure to do something if they're ever going to."

Mergers, say the airlines, could save the industry from mounting losses, bankruptcies, and global humiliation. "The U.S. airline industry is in serious decline!" writes James May, the president of the airline industry's lobbying body, the Air Transport Association, in an open letter entitled "Final Approach."

Below a chart comparing the paltry market capitalization of the six incumbent carriers with German carrier Lufthansa, May goes on to quote the pro-consolidation views of Morgan Stanley and J.P. Morgan analysts.

The July 27, 2001, announcement that rejected United Airlines' takeover of US Airways nevertheless looks controversial in hindsight. The September 11, 2001, terror attacks flung the airline industry into its deepest hole ever, and, in many ways, it has never fully recovered.

Borenstein says the Supreme Court has long stood by the idea that rules about the concentration of market power don't go out the window when an industry is suffering.

"So what?" he said. "The airlines are losing hundreds of millions of dollars because they happen to own aircraft when the price of oil went up."

In other words: If they lose, they lose.