Airlines are operating fewer flights this summer, meaning that planes are packed even with the slump in travel.
Often the airlines sell more tickets than there are seats on the plane. Last year, more than 63,000 passengers were bumped, according to government figures, and this year is shaping up as more of the same.
So what should you do if you get bumped? What if your flight is delayed so long that you miss your niece's wedding?
Before bargaining with the gate agent over travel vouchers and upgrades, it pays to know your rights and the airline's responsibilities.
The federal government sets rules on bumping and occasionally fines airlines for breaking them. This month, the Transportation Department fined Delta Air Lines $375,000, although it may waive about half if Delta improves its procedures for handling oversold flights.
Airlines must ask for volunteers first, and pay passengers who are bumped against their will.
If you are bumped from a domestic flight, the airline must pay you the price of a one-way ticket up to $400 cash if you are rescheduled to reach your destination between one and two hours of the original arrival time. The maximum doubles to $800 if it takes longer.
Some passengers with time to kill don't mind getting bumped. They hope to get cash, travel vouchers or an upgrade to first-class in exchange for taking a slightly later flight.
Chris McGinnis, a travel consultant in San Francisco, says the best flights to haggle over are late-afternoon or evening ones popular with business travelers who can't afford to be stranded overnight. Airlines are likely to offer more for passengers who give up a seat on a New York-Chicago run than on a flight full of vacationers from Atlanta to Orlando, he says.
Gate agents may put out a sign or simply tell passengers that they're looking for volunteers to skip the flight. McGinnis says it's often best to ignore their first offer and wait until departure time nears.
"The bidding gets stronger," he says. "That's when it goes from $100 off your next flight to maybe $300 and a business-class seat on the next flight out."
Experts warn about accepting travel vouchers. They might be hard to redeem, especially at peak travel periods. Make sure you understand any limitations.
Travelers are often baffled why airlines can sell more tickets than they have seats. Airlines oversell flights because some passengers buy costly fully refundable tickets on more than one flight and then only use one. Other flights are overbooked because the airline had to substitute a smaller plane with fewer seats.
While there are federal rules on bumping, there is no sweeping requirement for airlines to provide hotel rooms and meals for passengers who are stranded overnight, even if it's the carrier's fault, according to the Transportation Department. But you can haggle.
"It's up to the discretion of the carrier and the (gate) agent," says George Hobica, who operates airfarewatchdog.com. "Some airlines will do their best if you ask nicely and you ask privately you'll do better than if you make a scene." He says when a long delay appears obvious, you should ask to be rebooked on another airline.
Charlotte, N.C., real estate broker Mathew Bessette says Delta put him up in a hotel after his flight home from New York was canceled and a second flight spent four hours on the tarmac. He says he gained bargaining power by knowing the cause of the problem with his first flight no flight attendants.
"If their plane breaks down or their crew doesn't show up, that's their problem and it's their responsibility to accommodate you within reason," he says.
Veteran travelers say if a long delay will cause you to miss the reason for your trip a wedding or business meeting, for example ask for a refund. However, there is no law requiring the airline to give you a refund.
Airlines and passenger-rights groups are fighting over how the carriers handle long delays, and Congress may settle the issue. This month, a Senate committee passed a bill that would require airlines to let passengers off planes that are stuck on the tarmac for three hours.
The airlines say such a law would make things worse by forcing planes that might be near the front of the takeoff line to taxi back to the gate, then go to the back of the pack. More flights would be canceled, says David Castelveter, spokesman for the Air Transport Association, a Washington trade group for the largest U.S. carriers. Consumer groups aren't buying it.
"No one believes that the airlines will fix the problem themselves," says Kate Hanni, a California real estate agent who created a passenger-rights group after being stranded on a grounded American Airlines jet for more than eight hours in December 2006. "They haven't yet."
Since airline travel is often stressful, and summer always brings many delays, experts advise you have a Plan B. Know what flights are available if yours is canceled. If your flight is pushed back or scrubbed, hop on your laptop or phone to see if you can rebook.
"Prepare for the worst," says Hobica, the travel expert. "Bring a good book."