United Airlines, (also referred to as United Air Lines, Inc.) is one of the leading airlines of the United States, based in Chicago, Illinois. The airline is the second largest in the world by revenue-passenger-miles and the fourth largest in the world in terms of passengers transported. United Airlines operates scheduled passenger services to 210 destinations in 30 countries across North America, Asia, Latin America, the Caribbean, Oceania and Europe. The airline maintains a major hub at San Francisco International Airport with other hubs in Chicago, Denver, Los Angeles and Washington, D.C.
