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From https://www.transportation.gov/airconsumer/fly-rights#Overbooking

Involuntary Bumping

DOT requires each airline to give all passengers who are bumped involuntarily a written statement describing their rights and explaining how the carrier decides who gets on an oversold flight and who doesn’t. Those travelers who don’t get to fly are frequently entitled to denied boarding compensation in the form of a check or cash. The amount depends on the price of their ticket and the length of the delay:

If you are bumped involuntarily and the airline arranges substitute transportation that is scheduled to get you to your final destination (including later connections) within one hour of your original scheduled arrival time, there is no 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 200% of your one-way fare to your final destination that day, with a $675 maximum.
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 (400% of your one-way fare, $1350 maximum).
If your ticket does not show a fare (for example, a frequent-flyer award ticket or a ticket issued by a consolidator), your denied boarding compensation is based on the lowest cash, check or credit card payment charged for a ticket in the same class of service (e.g., coach, first class) on that flight.
You always get to keep your original ticket and use it on another flight. If you choose to make your own arrangements, you can request an “involuntary refund” for the ticket for the flight you were bumped from. The denied boarding compensation is essentially a payment for your inconvenience.
If you paid for optional services on your original flight (e.g., seat selection, checked baggage) and you did not receive those services on your substitute flight or were required to pay a second time, the airline that bumped you must refund those payments to you.