During weather emergencies and other unexpected occurrences, travel Web sites may not be able to update information fast enough to keep up with events. When demand is high, a hotel can ignore booking confirmations and give rooms to travelers who call directly or walk in off the street, says travel expert Parsons.

"It happens all the time. A confirmation number doesn't always assure you a room, especially during chaotic times such as during a hurricane," he said.

Hotels.com spokeswoman Nicole Hockin said the site is working on a new reservation system that would allow it to get more up-to-date information from more of its hotels. She said its system is in sync with the reservation systems of about 5,000 of the 10,000 hotels that appear on its site. In the next two months, Hockin said, the site will have a new system that will give more accurate room information on more of its hotels.

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