Airlines brought in $5.7 billion from fees for checked baggage and changed reservations in 2010, according to new data.
Revenue from checked bags totaled $3.4 billion, up 24 percent from the previous year, underscoring the fees' importance to airline profits.
"If it weren't for the fees, the airlines would most likely be losing money," said Jim Corridore, airline analyst with Standard & Poor's.
Delta Air Lines generated the most money from bag fees, $952 million. In 2010, Delta had a profit of $593 million.
Fort Worth-based American Airlines generated $580 million. United and Continental, which have merged, totaled nearly $655 million.
American generated another $471 million from fees for changing or canceling reservations.
American charges $25 each way for the first checked bag, $35 for the second and $100 for the next three. It charges $150 to change or cancel a reservation.
Airlines aggressively raised ticket prices early in the year. But those increases couldn't keep up with the rising price of jet fuel. Some more recent attempts at fare increases have failed because of passenger resistance.
So instead, 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 of FareCompare.com.
Staff writer Andrea Ahles contributed to this report, which includes material from The Associated Press.