Airlines overbook flights to compensate for passengers who simply don't turn up to travel - known in the trade as "no shows". However, when they get their estimates wrong there are not enough seats for everyone booked on the aircraft, so some passengers will have to travel at a different time. The Department of Transportation requires commercial airlines flying 30 passengers or more and originating in the United States to seek out volunteers before bumping anyone.
If you're not in a hurry and don't mind waiting another few hours to travel this can be to your advantage. Airlines use cash, vouchers and other rewards to attract volunteers. You may be offered free meals, free drink coupons and even an upgrade to business or first class if you will agree to travel on a later flight.
However, if you don't want to be bumped no matter how good the compensation, the golden rule is "check in for your flight as early as possible." If you can, do this online so you have a printed boarding pass when you arrive at the airport. Remember, it's the people at the back of the check-in queue who are most likely to find themselves waiting for a later flight whether they want to or not.
