Passengers have long complained about hidden charges that add to the cost of their journeys. Baggage and late check-in fees are just some ways airlines eke out more from their increasingly frustrated customers.
Now research has revealed how much airlines are actually taking in additional costs – and it looks like they're getting quite good at it.
Airline 'ancillary' revenue, or the amount made by airlines outside of their core transport operations, hit a record $82.2bn (£61bn) last year. That marks a massive 264% increase over the past seven years.
The report, by IdeaWorksCompany, shows that 10.6% of all airline revenue now comes from ancillary fees, with some budget carriers even more reliant on these charges.
Last year Ryanair made 26% of its revenues from ancillary charges, while the figure for Wizz Air was 39.4%.
The reports also claims that traditional airlines such as British Airways are making strong inroads in this area. The introduction of options for extra legroom, fast-track queueing and lounges has boosted company profits and added to choice for customers who don't mind paying a bit more.
"With few exceptions, airlines all over the world are moving to a la carte methods to provide more choices for consumers while boosting ancillary revenue," says the report. "For example, throughout North America, Europe, and Australasia, basic economy fares are now prevalent for short- and medium-haul travel."
The report suggests that ancillary charges are an important way for airlines to deliver profits in times of difficult trading. However, it warns airlines not to "simply charge new fees without creating a better product".
"The economic boon of ancillary revenue has proven to be a highly useful tool to fix airline finances. It delivers profit-boosting results during times of severe economic distress, and works effectively to lift profits even higher," the report claims.