Southwest raised fares $4 to $10 round trip, depending on the length of the trip, according to fare-tracking site FareCompare.com. And many other airlines have followed with similar increases.

United had filed for a comparable price boost earlier last week, then rolled it back on Thursday when other major carriers outside of Delta refused to follow.

United’s price increase last week — now driven by Southwest’s increase — was the 14th attempt by U.S. airlines to raise fares this year, as they’ve sought to deal with volatile jet fuel prices and post profits.