In a world of increasing add-on fees, enacted by airlines’ ongoing efforts to lower airfare while maintaining profitability, it can be difficult for travelers to keep up. Budget airlines began to lure passengers with no-frills prices and ridiculously low fares, but without all the bells and whistles that come with flying a major airline.

Rather than scouring the web for the answers, often hidden deep in an airline’s terms and conditions, here are the airlines that recently began charging the most for extra services — numbers that have grown steadily during the past 10 years.

Based on a report from IdeaWorksCompany, the airline charging the most in ancillary (extra) fees is Spirit, with an average extra charge of $51 per passenger. Rounding out the top five are Iceland-based WOW air ($49 per person), Allegiant Air ($49 per person), Frontier ($48 per person) and Jet2.com ($43 per person). The only major domestic airline to make the top 10 was United Airlines, with an average charge of $39 per person.

Unsurprisingly, the majority of the airlines on this list are budget airlines, making the bulk of revenue from extra fees, such as checked baggage, in-flight meals and seat selection. For Spirit at the top spot, nearly 47 percent of its revenue comes from these extra fees, 40 percent from baggage fees alone. Spirit also makes 33 percent of its revenue from online booking fees, also a large revenue stream for Allegiant Air.