Experts say consumers can expect to see more enticements to book directly, as airlines try to steer travelers to their own sites instead of online travel agencies, or OTAs, such as Expedia or Orbitz.

The feud is an old one: Airline sites offering fee-free booking had an edge over OTAs until just a few years ago, when OTAs began eliminating booking fees that added as much as $12 per ticket to fliers’ bills. Now, the lures include exclusive promotions, add-ons and, at least for Frontier, fee waivers. “It’s simple math,” says Rick Seaney, chief executive of comparison site Farecompare.com. “If it costs you, the airline, $16 to sell a ticket somewhere else and $2 on your own site, you have some money to play with.”