One-hundred-buck bag shows the true Spirit of Air Travel

It is only a matter of time before someone launches an airline called Suck-It-Up Air (Motto: "You get what you pay for—literally"). Thing is, it will probably do quite well. Budget carrier Spirit Airlines SAVE +2.49% provoked howls of protest this week, saying it would from November raise its already unusual fee for carry-on bags to $100 for anyone paying at the gate. Given that Spirit's passengers paid an average ticket price of $76.65 a flight in the first quarter, the new fee could see them paying more for the privilege of stuffing a bag into an overhead bin than for the privilege of squeezing themselves into the seat beneath. Rather than being a big money-spinner, though, the increased fee is more likely a form of deterrence. It will be an incentive for passengers to pay their fees ahead of time, says aviation consultant Bob Mann of R.W. Mann & Co. This reduces costly delays caused by bottlenecks at the gate. Despite the grumbling, Spirit is thriving. In the first quarter, it made an average of $51.68 in ancillary fees per person per flight, or 40% of passenger revenue, which was up 17.5% overall year-on-year. And as Ray Neidl, analyst at Maxim Group, points out, ancillary fees offer high margins. Since listing last May, Spirit's stock has almost doubled, far outpacing rivals—and oil. All airlines are trying to offset high fuel prices, be it by cutting unprofitable routes or even, in the case of Delta Air Lines, buying an oil refinery. Before the financial crisis and triple-digit oil prices, consumers became used to cutthroat airline competition that made leisure air travel commonplace. The resulting period of very cheap flights for all was unsustainable, as evidenced by recurrent bankruptcies and aging planes. Now, airlines are pricing their product more rationally. That is one reason big carriers are tussling with online-booking agents, such as American Airlines' spat with Expedia and Orbitz. After years of increasingly commoditized air services, airlines want to bring the customer relationship, and the associated margins, back in-house. Spirit's fee-charging forays are at the aggressive end of the spectrum but can be seen as part of this broader push toward price discovery for the various bits of the airline-service package. Above all, though, people are still buying. Spirit can be criticized for charging big nonticket fees to consumers already struggling with a new economic reality. But by offering them low ticket prices and options on other charges, Spirit looks perfectly aligned with the zeitgeist.