United Airlines Holdings, Inc. is a holding company, which engages in the provision of transportation services. The company is headquartered in Chicago, Illinois and currently employs 104,500 full-time employees. The company went IPO on 2006-01-25. The firm transports people and cargo throughout North America and to destinations in Asia, Europe, Africa, the Pacific, the Middle East and Latin America. The Company, through its wholly owned subsidiary, United Airlines, Inc., and its regional carriers, operates across six continents, with hubs at Chicago O'Hare International Airport (ORD), Denver International Airport (DEN), George Bush Intercontinental Airport (IAH), Los Angeles International Airport (LAX), Newark Liberty International Airport (EWR), San Francisco International Airport (SFO), Washington Dulles International Airport (IAD) and A.B. Won Pat International Airport (GUM). Its hub and spoke system allows it to transport passengers between various destinations with frequent services. The firm has contractual relationships with various regional carriers to provide regional aircraft service branded as United Express.