A roun-the-world ticket (also known as round-the-world fare or RTW ticket in short) is a product that enables travelers and tourists to fly and travel around the world for a relatively low price. RTW tickets have existed for some time and in the past were generally offered through marketing agreements between airlines on several continents. Now, they are almost exclusively offered by airline alliances such as SkyTeam, Star Alliance and Oneworld. They are priced according to class of service, origin of travel, mileage (usually between 20,000 and 40,000 miles), and sometimes season of travel. The traveler benefits from the large and optimised network of the airline alliance and can participate in the alliance's frequent flyer programs. However, these tickets are usually subject to restrictions. The start and end of the journey almost always have to be located in the same country and exactly one crossing each of the Atlantic and Pacific must be included in the itinerary. The number of stops is usually restricted to 5-15, and backtracking between continents (especially Europe/Asia) is often restricted. The dates and journey do not have to be pre-planned as travelers can change dates and destinations en route at a local office of any airline in the alliance (although a change of destinations often results in an additional fee, and if the next flight is left open-dated the booking can be dropped by the airlines' computers). Prices vary but are generally in the range of $3000-5000 USD.