Delta, United and Continental boosted fares Monday by up to $5 each way on many flights within the U.S.
It's the second increase in a week after more than two weeks when base fares remained largely unchanged.
That's bad news for travelers trying to book holiday-season trips. A Citigroup analyst says even before the latest fare increases, fares were already up to $70 higher than a year ago.
But J.P. Morgan analyst Jamie Baker says he'd be surprised to see low-fare carriers such as Southwest Airlines Co. match the increases. So it's possible this week's hikes could be rolled back.