Some airlines are keeping their New Year's resolution to raise fares.

FareCompare.com, a fare-tracking Web site, says United Airlines added as much as $10 round-trip to U.S. fares. Most of the increases United filed on Wednesday were $6 round-trip.

FareCompare says the other big airlines matched, except discounters Southwest, JetBlue, and AirTran. Rick Seaney of FareCompare says the price increases avoided routes that overlap with the cheaper airlines. The increases also don't apply to fare sales that are running through March.

Seaney says this makes four successful airfare hikes for 2009. Airlines have been eager to begin raising fares after using discounts to fill seats during the recession.