The online travel booking market is increasingly looking like the rest of the Web: Size, reach, and revenues are consolidating among few big players, and they are driving the spate of big acquisitions in the market.

The latest acquisition of Wotif by Expedia for $658 million is a continuum to the process that started couple of years ago.

The latest round of big stakes mergers and acquisitions arguably started in fall of 2012, when Priceline plunked down $1.8 billion for Kayak. Since then, the online booking market has become a two-horse race: Priceline Group vs. Expedia, as the rest of the old stalwarts like Travelocity and Orbitz, among others, have fallen way behind.

Add to that list HomeAway, TripAdvisor, and European consolidator eDreams Odigeo, and that rounds up the large acquirers in the online booking space in the last two years. Out of all of these, TripAdvisor is the outlier, having bought the most number of companies, but spent the least amount of money, focusing on tiny acquisitions.

We have collected the big four online travel acquirers — Priceline Group, Expedia Inc, HomeAway and TripAdvisor — and their acquisitions over the last two years — 2012-2014 — in a handy chart below:

CompanyPurchasedPriceYear
PricelineOpenTable$2.6 B2014
PricelineKayak$1.8 B2013
PricelineQlika$3 M2014
PricelineHotel Ninjasn/a2014
PricelineeBuddyn/a2013
PricelineBuuteeqn/a2014
ExpediaTrivago$632 M2013
ExpediaWotif$658 M2014
ExpediaAuto Escape Groupn/a2014
HomeAwayStayz Group$ 205.5 M for *2013
HomeAwayTravelmob.com*2013
HomeAwayBookabach*2013
HomeAwayToprural$16.2 million2013
HomeAwayGlad To Have Youn/a2014
TripAdvisorLaFourchetten/a2014
TripAdvisorVacationHomeRentalsn/a2014
TripAdvisorTripBodn/a2014
TripAdvisorWanderflyn/a2012
TripAdvisorOyster.com$34.8 M for *2013
TripAdvisorGateGuru*2013
TripAdvisorJetSetter*2013
TripAdvisorTinyPost*2013
TripAdvisorCruiseWise*2013
TripAdvisorNiumba*2013
Photo Credit: This consolidation in online travel market will only increase with mobile booking taking off. taymtaym / Flickr