Airlines' ancillary revenues grew 43% in 2009 over the previous year, to $13.5 billion worldwide, according to a study by IdeaWorks, a consultancy focused on airline ancillary revenues, that was underwritten by Amadeus.

Overall, airlines worldwide lost somewhere in the neighborhood of $16 billion in 2008 and nearly $10 billion in 2009.

The study noted that some of the additional revenue last year came from new ancillary revenue initiatives introduced by various airlines last year.

United overtook American in 2009 as the carrier that reported the most ancillary revenue, with $2.03 billion. In the summer of 2008, United introduced its Travel Options program, which allowed passengers to fast-track their way through airport lines or have their luggage shipped via Federal Express. It added new options last September, such as extra legroom and lounge access.

Outside the U.S., Qantas, with $1.04 billion, and Ryanair, with $882.5 million, were the ancillary revenue champions. Australia's Qantas was an early adopter of the fare family concept, and the Irish Ryanair is considered one of the world's fiercest unbundlers of air fares.

When it comes to how much ancillary revenue airlines collect per passenger, a different cast of characters shows up. Las Vegas-based Allegiant Air maintained its lead in 2009 by collecting an average of $33.10 per passenger in added fees. The only way to avoid a $14.99 booking fee on the carrier is by purchasing a ticket at the airport.

Jet2.com, a low-cost carrier in the U.K., bumped United out of the No. 2 spot in 2009 with a per-passenger average of $29.93. The carrier charges a minimum of $7.57 for online check-in, unless Solo or Visa Electron cards are used.

Allegiant also maintained its lead in the "ancillary revenue as percentage of total revenue" category in 2009, at 29.2%. Spirit Airlines overtook Ryanair for the No. 2 spot, with 23.9%.

Spirit is the carrier that introduced the imaginative "passenger usage fee:" A customer  buys a ticket, then pays a fee of $8 each way to use it, unless the purchase takes place at the airport.

Spirit also ruffled feathers this year when it began charging $20 to $45, depending on when the fee is paid, for carry-on luggage that does not fit under the seat.