Spirit Airlines, which instituted fees for carry-on bags in August 2010 and remains the only U.S. carrier to have adopted that policy, generated $50 million in revenue during the first year the fees were instituted, research firm IdeaWorks said in a report released Monday.

About one in five Spirit passengers have paid the carry-on fee, which helped Spirit increase its ancillary fees per passenger by 23% in 2011, to $43.04, IdeaWorks said, citing a Spirit Airlines investor presentation.

The carry-on fees range from $30 at the check-in counter for bags requiring overhead compartment stowage to $45 for bags checked at the departure gate.

Passengers with bags that can fit underneath a seat aren’t charged a fee.

Spirit, which has long promoted its low ticket prices, boosted ridership by 25% during the first year the carry-on fees were instituted.

Between 2006 and 2010, Spirit’s average ticket revenue fell $27, to $77.39, while ancillary revenue per passenger rose $30, from $5 to $35, according to the IdeaWorks report.

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