Travel search engines try to find every possible airfare or hotel rate for their customers, but they always come up short. Like every other travel website, they have content holes.

None of the travel search engines have access to the travel inventory of Travelocity or Expedia. Orbitz is available to Sidestep and Farechase, but not to Kayak. Several airlines and hotel chains have refused to sign compensation arrangements with the travel search engines, forcing them to find alternative ways to list their fares and room rates.

Sidestep, for example, sends customers wanting to buy a ticket on Northwest Airlines to Orbitz, where they have to pay a service fee. Kayak lists the Four Seasons Hotel among its Boston hotels but tells users they have to call the hotel to book or check rates.

David Cush, vice president and general sales manager at American Airlines, said travel search engines are fairly comprehensive on domestic airfares, but less so abroad because there are so many more airlines with whom they need to negotiate deals.

Get the full story at The Boston Globe