The nation's airlines have failed the last few times they tried to raise fares, but they're not giving up.

Delta Air Lines Inc. added $10 per round trip for most of its U.S. routes, a spokesman for the Atlanta company confirmed on Monday.

Rick Seaney, the CEO of FareCompare.com, said it was the 11th attempt to raise base fares this year and the last four failed because some airlines declined to go along.

Airlines say they need higher fares to cover rising costs for jet fuel. But they've been undercutting recent fare increases by offering a slew of sales, including some for peak summer travel.