Last year U.S. hotels collected more than $2.5 billion in fees and surcharges, up from $2.45 billion in 2015 according to research by Bjorn Hanson, a professor at New York University’s Tisch Center for Hospitality and Tourism.

Hanson credits the uptick to the nation’s thriving travel industry. “When times are financially difficult, hotels are more concerned about offending guests with extra charges, but when the economy is doing well hotels feel more confident about increasing their fees,” says Hanson, who has tracked U.S. hotel fees and surcharges data since 2000.

Unfortunately for travelers, many hotel fees are often buried in lengthy disclosure statements or tucked into bill summaries at checkout.

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