There is no limit to the amount of money an airline can offer a passenger who agrees to be bumped from a flight. In the past, passengers have received $10,000 in travel credit when bumped.
This is unlikely however, and you should expect closer to $400-$500 in travel credit if you are bumped from a flight.
This is what you should know if you are forcibly or voluntarily bumped from a flight:
Under federal law, airlines must compensate you in cash if you are forcibly bumped from a flight, with the amount varying depending on the length of the delay and the price of a one-way ticket.
(For a one to four hour delay on international flights, 200% of the one-way fare, but no more than $675. For a more than four hour delay on international flights, 400% of the one-way fare, but no more than $1,350. Department of Transportation)
If you volunteer to be bumped from a flight, the rules are a little different.
The airline will likely offer you a travel voucher instead of cash, which can be a good or bad thing depending on how often you fly. If you don’t fly very often, you should ask for cash, as vouchers expire after a year and have other restrictions like black-out dates. However, if you fly often, you may get a better value with a voucher.
Before you agree to a deal, make sure that you have a confirmed seat on your new flight and that you’re not standby. You could also ask for a window or aisle seat while you’re at it, and a restaurant voucher to enjoy during your delay. (If you won’t be flying until the next day, ask for a hotel voucher for the night.)