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Just in time for the holidays, an airfare watchdog says the major airlines have raised fares as much as $10 each way, although it is not yet clear whether the price hike will stick.

Rick Seaney of FareCompare.com said Delta Air Lines lead the way Tuesday afternoon with an increase of $4 to $10 each way for flights within the U.S. They were matched that night by American Airlines and U.S. Airways. United began matching Wednesday and American raised several hundred thousand additional fares.

However, such increases are often rolled back if other airlines — especially Southwest — don't match them. That's because airline customers will book elsewhere if one airline's tickets cost more than competitors' fares. So far there's been no activity from Southwest or JetBlue 

"For the upcoming peak holiday period the gap between base and market selling prices for the most convenient itineraries is the highest we have tracked," said Seaney.

And it's not just their ticket's face value consumers should keep an eye on. "Carriers continue to get incrementally better at monetizing their sushi menu of add on fees," he added.

Seaney counts 12 attempted fare increases by U.S. airlines this year, but he says only three of those have succeeded. The last time domestic airlines were successful at hiking airfare in December was 2010, when oil prices were in the low $90's per barrel. Currently oil is trading at $98 per barrel.

The Associated Press contributed to this report.