Airlines again are seeking to boost round-trip ticket prices US$10 on many domestic routes, while quietly offering huge limited-time discounts between other U.S. cities.

US Airways on Thursday raised most of its domestic round-trip fares by US$10, and three competing airlines - Delta, American and Continental - matched the increase Thursday and Friday.

It was the 10th attempted rise in fares this year by airlines, which have been raising prices to meet escalating jet-fuel prices, says Rick Seaney, CEO of FareCompare.com, who closely monitors airfares.

On March 1, American Airlines successfully raised most domestic round-trip fares US$10 - the sixth successful attempt to raise fares US$4 to US$10 this year, Seaney says. If the current increase sticks, it would be the seventh since Jan. 1.

American, United Airlines and Continental Airlines made three subsequent attempts in March to raise fares US$10, but the increases didn't stick, because other airlines didn't match the prices, he says.

While fares on many routes went up US$10 last week, there were huge price reductions on others. Some price drops lasted less than a day, and the number of tickets sold at bargain prices was limited.

"There have been epic, unadvertised fare wars that have lowered other fares by hundreds of dollars on hundreds of routes," says George Hobica, founder of Airfarewatchdog.com.

United and Continental on Thursday cut prices in half on various routes, Hobica says, but many of the 50% cuts were not in effect on Friday afternoon.

For a limited time late last week, United and Continental sold Baltimore-Phoenix and Buffalo-Las Vegas round-trip tickets for US$118, according to Airfarewatchdog.com.

Also during a limited time last week, American sold round-trip tickets to Honolulu from Washington, Newark or Cleveland for US$391 - a nearly 50% discount. On Friday, Southwest Airlines offered some round-trip tickets from Newark to San Francisco or San Diego for US$158, according to Airfarewatchdog.com.

"The unadvertised sales typically last two to eight hours, but some lasted overnight," Hobica says.

To get such deals, fliers should subscribe to fare alerts provided free by Airfarewatchdog.com, FareCompare.com or other travel websites, Hobica says. Consumers who don't act immediately to book an unadvertised fare sale may be stuck with an unappealing fare. Average fares so far this year rose 12% to 14% compared with the same period last year, Hobica says.