United Airlines, Inc., commonly referred to as United, is a major American airline headquartered in Chicago, Illinois. It is the world's third-largest airline when measured by revenue, operates a domestic and international route network, and has presence in the Asia-Pacific region. United is a founding member of Star Alliance, the world's largest airline alliance. Regional service is operated by independent carriers under the brand name United Express. Its main competitors are American Airlines, Delta Air Lines, and Southwest Airlines.
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