Delta Air Lines asks more than 10 out of every 10,000 passengers to voluntarily surrender their seat and take a later flight, dubbing it the major U.S. carrier most likely to bump passengers.

Bumping occurs when airlines oversell flights to avoid flying with empty seats due to no-shows, or when the carrier is forced to switch to smaller planes due to delays or equipment problems.

United Airlines and Southwest Airlines were other carriers that frequently bumped passengers in 2016, shifting an average of 7.7 and 7.2, respectively, of every 10,000 passengers to different flights. The research, conducted by milecards.com, reports on airline credit card and rewards programs.

The report includes U.S. airlines that have at least 1 percent of total domestic scheduled service passenger revenues and operate aircraft with a passenger capacity of 30 or more seats, providing system data for scheduled passenger service on domestic flights and data on international flight segments on United States-originated flights.

The report states travelers most likely to get bumped, 15.9 per 10,000 passengers, are those on smaller, regional airlines. Most passengers gave up their seats willingly, while only 8.3 percent did so involuntarily. Overall, the rate at which airlines bumped passengers declined 40 percent between 2010 and 2016.

JetBlue, Frontier and Hawaiian Airlines are a few with the lowest bump rate and benefit from serving far more leisure travelers than business travelers — since they are more apt to change travel plans with little notice.