Priceline's (PCLN) decision to buy the Amsterdam-based website has proved to be the most lucrative acquisition in the history of online travel. It's outdone Internet mogul Barry Diller's acquisition of travel websites and in 2003. Eight years later, more than 60% of Priceline's bookings come from Europe, mostly via Priceline boasts revenue for its most recent four quarters ended Q1 of $5.53 billion vs. $4.23 billion for Diller's Expedia (EXPE), its nearest rival. Priceline is set to report Q2 results on Aug. 8. " is pretty obviously the most important single business within Priceline," said S&P Capital IQ equity analyst Scott Kessler. Priceline doesn't break out revenue. But Kessler says that based on geographic data disclosed by Priceline, about half of Priceline's revenue is funneled through's home country of the Netherlands. This, he says, gives a pretty good idea of the unit's importance. Get the full story at Read also "Morgan Stanley Ups to Buy on" at Barron's and "Expedia admits that TripAdvisor and are hurting it hard" at Tnooz