Airlines are imposing the first fare increase of the new year.

Increases on many domestic routes range from $4 to $10 per round-trip ticket. Southwest Airlines raised prices on most of its routes, according to Rick Seaney, chief executive of Other major airlines followed suit, including American, Delta, United, Continental, US Airways and Frontier.

The increase mostly covers the usually slow travel period in January and February, and comes as the airlines are grappling with higher prices for jet fuel. U.S. airlines lost billions in 2008 and 2009 but turned profitable last year.

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