If you’ve flown this past spring and summer, you’ve probably noticed fuller flights. Hate to tell you this, but with two major holidays approaching – Thanksgiving and Christmas – expect more of the same.

For airline passengers, it means a greater chance of getting involuntarily bumped from a flight, continuing an already worrisome trend.

A lot of the bumping happens because airlines overbook, counting on some folks not making their fight.

Overbooking is not illegal; however the Department of Transportation does require airlines to ask for volunteers when bumping is necessary. But how much you get for giving up your seat varies from airline to airline.

Southwest Airlines, which bumped more than 5,400 passengers from January to June, offers volunteers the cost of the ticket for the leg of the trip from which they are bumped. The airline also offers a $100 travel credit if volunteers can take the next available flight and $200 for the flight after that.

So what’s a passenger to do if bumped involuntarily?

The airlines do have to follow certain guidelines required by the Federal Aviation Administration. (You can find information about all your rights as a passenger by going to www.dot.gov. In the search field put “Fly-Rights.”) If you are forced to give up your seat, here’s a summary of some of your rights as outlined by the DOT:

¢ If the airline can arrange for you to get on another flight that will get you to your final destination (including later connections) within one hour of your original scheduled arrival time, there is no required compensation.

¢ If the airline arranges substitute transportation that is scheduled to arrive at your destination between one and two hours after your original arrival time (between one and four hours on international flights), the airline must pay you an amount equal to your one-way fare to your final destination. Unfortunately, the amount the airline has to pay is capped at $200.

¢ If the substitute transportation is scheduled to get you to your destination more than two hours later (four hours internationally), or if the airline does not make any substitute travel arrangements for you, the compensation doubles. In this case the maximum is $400.

¢ You always get to keep your original ticket and use it on another flight. If you decide to make your own alternate travel arrangements, you can ask for a refund on the ticket for the flight you were bumped from.

To be compensated, you must have a confirmed reservation. Look for an “OK” on your ticket.

You also have to meet the airline’s deadline for buying your ticket.

In addition to the ticketing deadline, each airline has a check-in deadline that you need to meet. If you want to decrease the chances of being bumped, get to the airport early or check in online as soon as you are allowed, typically 24 hours before the flight. On oversold flights, the last passenger to check in is usually the first to be bumped.