Fewer passengers were bumped off their flights in 2017 than at any point in over the last twenty years.

On average, about .34 passengers were bumped for every 10,000 that flew in 2017, according to data compiled by the U.S. Department of Transportation. That's about half the 2016 rate of .62 bumps per 10,000 passengers. The 2017 rate is the lowest on record since 1995, the agency said.

About 681 million people traveled on the 12 biggest U.S. airlines last year, 20 million more than the year before.

The figures include flyers who agreed to be bumped, meaning that the airline gave them cash or other incentives to voluntarily give up their seat, as well as those who were denied boarding by airline officials.

All the ways you could lose your seat on an airplane

Passengers get bumped off of flights for a lot of reasons. The flight might be oversold, or there could be a safety or mechanical issue with your plane requiring a downgrade to a smaller aircraft. Airlines might have to make space for employees to travel, or you may be breaking the rules.

The forcible removal of passenger Dr. David Dao from a United Airlines regional flight in April 2017 triggered public outrage and shifted how airlines approach bumping.

After the incident, United (UAL)overhauled its policies in order to reduce involuntary denial of boarding "to as close to zero as possible."

Delta (DAL)Air Lines and United significantly increased the financial incentives fliers get to give up a seat, while Southwest (LUV)Airlines vowed to phase out overbooking altogether.