Two of the largest US airlines raised fares on Friday, aiming to take advantage of strong travel demand to boost profitability and offset the price of jet fuel, which despite recent declines, remains historically high.

American Airlines and Delta Air Lines said they raised fares USD$5 each way on most routes.

The move has yet to be matched throughout the industry, but if other airlines follow, it will mark the second successful fare increase this year.

A combination of increased demand and reduced capacity has pushed fares higher over the past 14 months after several years of steady or declining prices.

Airlines are also looking to offset relatively high fuel costs, despite a 15 percent decline in the price of crude oil since February 2006.

"At this point, fuel is not the clear driving force for increases as it was in 2006," said Neil Bainton of air fare research firm FareCompare. "Instead it is an effort by the airlines to improve profitability under market conditions with strong demand and decreased capacity."

Crude oil futures traded slightly down at USD$57.30 a barrel in New York on Friday.

Despite recent declines, airlines say they continue to face big operating expenses.

"We continue to face increased costs, including fuel," a Delta spokeswoman said. The airline initiated the fare increase on Thursday night with an increase of USD$5 each way systemwide. American matched on Friday.

Delta's November operating report, the most recent it has released, showed jet fuel was the carrier's biggest expense, followed closely by salaries and related costs.

American's quarterly earnings report showed it paid less for fuel in the fourth quarter than it did a year earlier. Jet fuel was its second-largest expense after labor costs.

United Airlines, Continental Airlines and bankrupt Northwest Airlines said they were studying the increase.