Denver -- For about 45 minutes, United Airlines' tickets simply could not be undersold.
Visitors to the airline's Web site Tuesday were able to buy roundtrip tickets across the nation for $25 due to an error by a computer that distributes fares for major airlines.
United said it will honor the tickets, but did not know how many were bought or the destinations, said spokeswoman Chris Nardella.
"We discovered the problem and we fixed it, but there was a 45-minute window when customers were able to book these tickets," she said.
The problem occurred when ATP Co., a clearinghouse for all airlines' fares, loaded new sale fares onto United's site and accidentally put up incorrect prices, Nardella said.
It wasn't the first time United sold tickets so cheaply via the Internet. In January, 142 passengers bought tickets to international destinations for as little as $25.
United first said it would not honor those fares -- also the result of a technical problem -- but later agreed to do so.
