(CNBC) — Record numbers of travelers are taking to the skies. So what happens if there’s no seat for you?

Airlines have for years sold more seats than they have on board, a legal practice that has allowed them to manage inventory: No airline wants a seat to go empty if a traveler cancels at the last minute.

Luckily, the rate of airline bumping has declined in recent years to a record low. Last year, U.S. airlines denied boarding to 0.3 people per 10,000 passengers, according to the U.S. Department of Transportation.