The figures for April 2008 from web traffic analysis service Compete.com indicated sister site in the Expedia Inc stable, Hotels.com, also secures a further 11% of all outbound clicks from Tripadvisor.com.
Data for upstream referrals from hotel search pages on the UK version of Tripadvisor are currently not available.
The figures have highlighted how important the Expedia-Tripadvisor relationship has become commercially to both parties despite continued pledges of independence by the user review giant.
Critics of the affiliation have suggested in the past that Tripadvisor favours ads for its parent company despite the system working on a Google-style pay-per-click model.
Tripadvisor confirmed to Travolution that Expedia is “one of the biggest advertisers” on the site but would not comment on how much is spent and what percentage of its search ad revenue is contributed by Expedia.
Expedia Inc bought the Tripadvisor in 2004 but the companies are still run from separate locations and with different management teams.