Around 20 years ago, no one had even heard of OTAs. The concept was slowly developing with Microsoft launching Expedia Travel Services in 1996 in the USA, followed by its European counterpart, Priceline, in 1996. Both platforms allowed customers to book their holidays online. First perceived as a dubious tool for booking, the trend quickly evolved, with booking services expanding from initially hotels only to cars, flights, cruises, restaurants and holiday packages. In 2013, travel sales generated by OTAs accounted for around 45% of total European travel sales revenue (Euromonitor, 2013), of which 76% was generated by the two major players, Priceline and Expedia (82% and 18%, respectively, emphasizing the substantially stronger market presence of Priceline in Europe owing to its strong presence with Booking.com). However, this development took place at the expense of direct bookings and traditional travel agency bookings. Although OTAs still achieve the lowest market share in terms of travel sales revenue amongst all distribution channels, they have recorded the strongest growth in revenue and average rate for several consecutive quarters (TravelClick, 2015).

The most significant players amongst OTAs are Expedia and Priceline (better known for its European branch, Booking.com). With Expedia's acquisition of Travelocity in January 2015 and Orbitz Worldwide shortly thereafter, Expedia2 gained first position in terms of worldwide gross bookings, whereas Priceline remains the largest OTA by revenue (collecting on average US$0.17 per dollar booked compared to US$0.12 for Expedia).