Frontier now gets about 30 percent of its revenue through online bookings but hopes to increase that to 50 percent in the next year.

Bob Rapp, CIO of Denver-based Frontier, said the change is part a strategy to improve Web site functionality and performance and to encourage customers to use the site with incentives such as free in-flight TV for people who book online. "The underlying technology was really meant as getting us a foundation in which we can grow," he said.

The industry leader in online bookings is JetBlue Airways Corp., which at the end of 2005 reported that 77 percent of its bookings come through its Web site. Analysts expect that number to grow.

An airline's Web site "is incredibly critical to an airline's survival because financially, the cost of a sale through a Web site is generally much lower," said Henry Harteveldt, an analyst at Forrester Research Inc. in Cambridge, Mass.

Processing a booking through a Web site can cost an airline less than a US$1, while a reservation booked through a call center can cost between $8 and $16, said Harteveldt. It means airlines need to provide customers with a good online experience, he said.