Moving to further grow its already expansive ad-driven business model, TripAdvisor.com introduced a metasearch flight tool that for the first time would enable users to make side-by-side comparisons of fares offered by competitors Expedia.com, Hotwire and Travelocity.

TripAdvisor's new product, which Travel Weekly viewed just before it was introduced in a beta test, employs ITA Software, Sabre, Amadeus, Expedia.com, Hotwire.com and Travelocity.com to search for fares.

It also introduces a feature called Fees Estimator, which enables consumers to compare the costs of optional services, ranging from checked bags and in-flight entertainment to meals. TripAdvisor claims that Fees Estimator, which it developed in-house, is the first tool to go live that enables consumers to view total flight costs before booking.

User-generated content from TripAdvisor's SeatGuru enables consumers to consider an aircraft's seat dimensions, storage space, video screen viewability and in-flight amenities.

"We are changing the category," said Bryan Saltzburg, a former Travelocity official who is general manager of new initiatives at Expedia-owned TripAdvisor. As proof of that assertion, he cited the transparency of Fees Estimator and the joint participation of competitors Expedia.com and Travelocity.

"Expedia and Travelocity have never played together," he said.

As for the expanded air focus, he said, "We strongly believe that this is a natural evolution of what TripAdvisor is about."

TripAdvisor, which claims 23 million monthly unique visitors to its network of sites, made its reputation featuring traveler-written reviews of hotels and restaurants, making its money off travel agency and supplier advertising framing its pages.

Before introducing its new product, TripAdvisor already enabled consumers to search for flights using the search engines of one advertiser at a time. Expanding into the comparative-shopping arena of meta-search, where consumers can view fares from various sources in a single grid, gives TripAdvisor a new channel for its advertising business.

Across the travel industry, companies are attempting to introduce or enhance their ad revenue streams. TripAdvisor saw its global media revenue increase 48% in 2008, to $299 million.

Its first foray into metasearch, which follows by a few weeks Travelzoo's introduction of the metasearch site Fly.com, is expected to be among a series of metasearch introductions by travel companies over the next few months.

TripAdvisor's metasearch site is notable for a number of firsts, according to company officials. Most importantly, it marks the first time that Expedia and Hotwire have agreed to participate in a metasearch service.

And, given Travelocity's participation, it marks the first time that these major online-agency rivals have agreed to allow a metasearch service to display their results side by side with their competitors.

TripAdvisor's initiative, too, signals the first time a company (Expedia Inc.) that owns an online agency (Expedia.com) has introduced a metasearch product. Metasearch was long viewed primarily as a supplier channel that competed with OTAs.

Consumers can click on the TripAdvisor flights tab, enter city pairs and dates and view fares from Continental or Spirit, for instance, along with those from Expedia.com, Hotwire.com and Travelocity.

The fares from airline sites and Hotwire often are a tad lower than those from Expedia and Travelocity because the airline sites and Hotwire generally don't charge service fees to consumers, while Expedia and Travelocity do.

Travelocity long resisted metasearch, arguing that comparative shopping sites commoditized travel and chipped away at brand value. The change of heart is a result of the volume of traffic TripAdvisor can drive to Travelocity.com's ads.

"First, it's important to note that we view this as an advertising deal," said Travelocity spokesman Joel Frey. "We are not redistributing or displaying content on TripAdvisor. It is just a text link that takes the user back to Travelocity for details and booking.

"We know we've got great pricing and a strong value proposition associated with our brand, so meta is simply another marketing channel."

Saltzburg was coy about how TripAdvisor uses ITA Software, Amadeus, Sabre and the online agencies for searching or how TripAdvisor persuaded Expedia.com and Travelocity to participate.

"I can't give you the secret sauce," he said.

Saltzburg noted that Sabre and Amadeus host airlines and power various agency sites. ITA Software powers flight schedules, fares and availability searches for numerous industry players.

Saltzburg was vague about the business model, as well, other than to say that it's an advertising play. Every airline or other participant in the company's metasearch program has an advertising relationship either with TripAdvisor itself or with Sabre, Amadeus, Expedia.com, Hotwire, Travelocity or other partners, he said. With that requirement, all major airlines, with the exception of a handful like Southwest, are present in search results.

"We are OTA and airline-partner agnostic," Saltzburg said, meaning that display results aren't skewed to sister companies Expedia.com and Hotwire or to airline advertisers, for instance.

Saltzburg declined to say if TripAdvisor would introduce a metasearch product for hotels and car rentals, but he hinted that the new product could add traveler reviews of air products.

For now, TripAdvisor's metasearch feature, which includes international flights, was to be released in the U.S. only. However, the company also has a presence in nine other countries in Europe and Asia.

"We have a global footprint, and we think globally," Saltzburg said.