Global online travel sales have grown over the past few years. Online sales value of air travel, hotels and OTA's are all expected to grow by at least six percent in 2015. In the following year, online travel sales cumulatively generated 564.9 billion U.S. dollars. This figure was forecasted to grow to 817.5 billion U.S. dollars by 2020. In 2015, the largest share of online travel sales were conducted in North America, the U.S. alone generated around 168 billion U.S. dollars through mobile and desktop travel sales. This figure was forecasted to grow annually until 2019. In terms of sales, Expedia Inc. was the largest travel agent in the world, followed by the Priceline Group, highlighting the threat OTA's pose to traditional travel agencies. Online travel booking has been increasing in the United States. Between the spring of 2008 and the spring of 2016, the number of internet users who managed travel reservations online increased from around 40.6 million to 64 million.
Travelers are also relying more on travel review sites when booking. The share of U.S. travelers who said travel review sites influence their travel choices increased by 10 percent between 2014 and 2015. The leading travel site used in United States based on number of visits was, however, not an online travel agency. As of October 2016, TripAdvisor, which operates primarily as a review site, gained the highest share of travel website visits with 13.8 percent.