This increasingly puts TripAdvisor in competition with its two largest advertising partners, Expedia and Priceline, that have so far declined to participate in the booking program. Additionally, these OTAs may dial back their advertising spend on TripAdvisor, meaning it will be increasingly reliant on these transactions. Transaction revenue is likely to become an increasingly important revenue growth driver over the next few years. According to CEO Stephan Kaufer, the company expects "the hotel space to migrate towards transaction, but where I see vacation rentals being in the future, I would expect it to be almost all transaction oriented." TripAdvisor's Q2 report showed how accelerating growth in Instant Booking is boosting its contribution to overall revenue, while increased advertising spends to promote the service ate into the bottom line. Yet, its foray into booking is in time likely to lead to decreased advertising spend from its two largest customers, Priceline and Expedia, as it increasingly becomes a competitor as well as an advertising partner. Although it is on the right track in terms of growth, it will need to see a significant bottom line contribution from Instant Booking fairly soon. Get the full story at Seeking Alpha