NEW YORK — United Airlines, the second-largest U.S. carrier, raised domestic fares by $10 to $20 round-trip to offset rising fuel costs, a spokeswoman said Friday.

The move marks the first widespread increase by a leading carrier this year, and is the latest in a series airlines have attempted in recent months as the price of jet fuel soared.

"Unfortunately for travelers in 2008 this increase is most likely going to be matched quickly and will probably be the first in a continued wave of increases," said Rick Seaney, chief executive of, in an interview.

United's increase affects nearly all domestic routes, spokeswoman Robin Urbanski said. Tickets on short flights will cost $5 more one-way, while flights of more than 1,500 miles — such as Chicago to Las Vegas or Boston to Denver — will cost travelers $10 more one-way, she said.

Urbanski said the Chicago-based airline raised prices in an effort to "offset the unprecedented price of fuel."

Days before Christmas, United doubled a $5 fuel surcharge it added a month earlier, effectively raising round-trip fares by $10. Urbanski said that surcharge remains in place in markets where it was matched by competitors.

"Fares are slightly higher in some markets but overall, fares are still relatively lower than a few years ago given that fuel is our highest expense," she added.

Carriers tried 23 times to raise fares in 2007, according to data compiled by, which tracks airfare changes. Of those, 17 were matched by competitors and remained in place for more than a week, Seaney said.

Shares of UAL Corp., United's parent, fell $1.49, or 4.7 percent, to $30.26 in morning trading.