How much will an airline charge for a flight? As much as it can get, or at least as much as the competition will allow.

On Thursday United Airlines raised fares $10 on pricey round-trip flights business travelers buy within seven days of departure. American Airlines and Delta Air Lines matched the increase.

And by Monday, all three airlines had abandoned the fare hike.

"We rescinded because we did not see other airlines match the increase," United spokeswoman Robin Urbanski said. "We rescinded to remain competitive."

The issue of pricing is a sensitive one, not just because the airline business is fiercely competitive, but because carriers feel they can't say too much about their intentions. If they do it could lead to charges that an airline was trying to signal other carriers to join in fare hikes, a potential violation of antitrust laws.

"We have to be careful talking about this," said American spokesman Tim Wagner. Wagner, too, said the increase wasn't matched by enough other airlines, and so was not competitive.

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