NEW YORK -- Passengers hate them, but airlines can't afford to give them up -- those irritating bag fees.

U.S. airlines collected $3.4 billion for checked luggage last year, according to a government report issued Monday. That's up 24 percent from 2009 and a big reason the industry made money again after three years of losses.

In 2010, the major airlines made a combined $2.6 billion in profits, less than they collected in bag fees. The fees -- typically $50 round trip for the first piece of checked luggage and $70 for the second -- allow the industry to navigate between rising fuel costs and customers who expect rock-bottom airfares.

"If it weren't for the fees, the airlines would most likely be losing money," said Jim Corridore, airline analyst with Standard & Poor's.

That's little comfort to fliers who have increasingly felt nickel-and-dimed by the airlines and now face a summer of higher airfares and packed planes.

"I feel like I am constantly being hit by little things by the airlines," said Lauren DiMarco, a stay-at-home mother from Wenham, Mass. "We're already paying so much money."

Delta Air Lines generated the most revenue from bag fees -- $952 million -- followed by the combined United and Continental airlines at nearly $655 million. American Airlines collected $580 million and US Airways $513 million, according to the Department of Transportation. None of those fees is subject to tax.

Airlines aggressively raised ticket prices early in the year. But those increases couldn't keep up with the price of jet fuel, now 37 percent more than last year. Some more recent attempts to raise fares have failed because passengers balked at paying more.

So the airlines focus on fees.

"Unfortunately for the airlines, when they try to roll $50 into the ticket prices, people stop buying tickets," said Rick Seaney chief executive officer of FareCompare.com.

Delta and United raised fees this month to check a second bag to Europe. Delta also added a fee for second bags checked to Latin America and ended its $2 discount for paying fees in advance online.

Last week, several airlines did remove excess-baggage fees for the military after Delta charged a group of 14 soldiers returning from Afghanistan $200 each. A YouTube video of two of the soldiers complaining was viewed almost 200,000 times in one day.

American Airlines introduced fees for the first checked bag in 2008 as the price of oil skyrocketed. The other airlines, except JetBlue and Southwest, have since followed and progressively increased those charges. Southwest has used its refusal to charge fees as a marketing tool.

Many fliers are still unaware of the fees or don't realize how much they have to pay until they arrive at the airport ticket counter.

"They find out very quickly when they are asked to pull out their credit card," Mr. Seaney said.

The airlines aren't alone in charging fees that irk customers. For instance, banks charge customers to use out-of-network ATMs and levy fees for insufficient balances. But there is something especially irritating about paying a fee just before you board a plane for your long-awaited vacation.

Buoyed by the success with bag fees, the airlines are charging for all sorts of extras. All of these fees add up to about 6 to 7 percent of overall airline revenue. New rules from the Department of Transportation will require airlines, starting Aug. 23, to "prominently disclose all potential fees" on their Web sites prior to a ticket purchase. In the meantime, fliers just need to do their research before heading to the airport.

First Published June 14, 2011, 4:30 a.m.