Airline baggage fees bring in billions of dollars annually.

With most major carriers charging passengers fees for baggage, U.S. airlines racked up more than $4.5 billion in bag fee revenue in 2017. That's up from nearly $4.2 billion in 2016, according to the U.S. Bureau of Transportation Statistics.

For the most part, the biggest airlines brought in the most in bag fee revenue.

American Airlines had the highest total of about $1.1 billion in bag fee revenue last year, followed by Atlanta-based Delta Air Lines at $907.6 million.

United Airlines’ bag fee revenue totaled $794.5 million in 2017.

Ultra low-cost carriers Spirit Airlines and Frontier Airlines, which charge for both checked and carry-on bags, came in 4th and 5th for baggage fee revenue. Spirit's total for 2017 was $492.6 million, while Frontier's was $364.1 million.

Southwest Airlines, which allows passengers to check two bags for free, collected $46.1 million in bag fees in 2017. That put it at 11th out of 13 carriers ranked by baggage fee collections. Dallas-based Southwest is the second-largest carrier at Hartsfield-Jackson International Airport.