Almost 54% of our $835 million valuation for Kayak comes from advertising by our analysis. While online travel agencies like Expedia and Priceline provide online bookings for hotels, airlines, car rentals and vacation packages to consumers, Kayak provides comprehensive research for best fares along with other value-added services like flight status updates and pricing alerts. The company’s online ad revenues have seen a positive growth since past few years except in 2009, where the growth rate declined due to recessionary macroeconomic outlook and a tighter advertising budget. Kayak sources majority of its airfare query results from data licensed by ITA software, which was recently acquired by Google, and this has put Kayak’s IPO launch in doldrums and is also raising concerns on its future advertising revenues and margins. But, for now, Kayak enjoys tremendous popularity in the U.S. and internationally with its airline and hotel booking queries seeing a consistent uptick. Get the full story at Forbes