After adding fees for things like bag checks, seat assignments, pillows and blankets, there simply aren't many more complimentary items and services airlines can pry loose from the base fare, experts say.
That's welcome news for travelers who find the avalanche of new fees tedious.
"If people knew that this was the extent to which this is going to go, that would make them feel better," said Kevin Mitchell, chairman of the Business Travel Coalition (BTC). "(But) they should also know that there's no reversing it."
Mitchell also noted that airlines are creative and that there may yet be some elements of the reservation or check-in process that they can still unbundle.
Major airlines, battered in recent years by high costs, low-fare competition and economic recession, have generated billions of dollars in new revenue from sales of items and services that previously had been free.
Last year, for example, airlines unveiled a particularly unpopular charge, for checking a single bag. Passengers balked, but now that fee is common among major U.S. carriers like AMR Corp's American Airlines and UAL Corp's United Airlines.