United Airlines Holdings, Inc. (formerly known as United Continental Holdings, Inc., UAL Corporation, Allegis Corporation and founded originally as UAL, Inc.) is a publicly traded airline holding company headquartered in the Willis Tower in Chicago. UAH owns and operates United Airlines, Inc. UAL Corporation agreed to change its name to United Continental Holdings in May 2010, when an agreement was reached between United and Continental Airlines where United would acquire Continental. To effect the acquisition, Continental shareholders received 1.05 shares of UAL stock for each Continental share; at the time of closing, it was estimated that United shareholders owned 55% of the merged entity and Continental shareholders owned 45%. The company or its subsidiary airlines also have several other subsidiaries. Once completely combined, United became the world's largest airline, as measured by revenue passenger miles. United is a founding member of the Star Alliance. UAH has major operations at Chicago–O'Hare, Denver, Guam, Houston–Intercontinental, Los Angeles, Newark (New Jersey), San Francisco, and Washington–Dulles. Additionally, UAH's United is the largest U.S. carrier to the People's Republic of China and maintains a large operation throughout Asia. UAH uses Continental's operating certificate and United's repair station certificate, having been approved by the FAA on November 30, 2011. On June 27, 2019, the name of the parent company was changed from United Continental Holdings to United Airlines Holdings. Major subsidiaries The following is the list of major subsidiaries of United Airlines Holdings, Inc. United Airlines, Inc. (formerly Continental Airlines, Inc.) Air Micronesia, Inc. Continental Micronesia, Inc. CAL Cargo, S.A. de C.V. CALFINCO Inc. Century Casualty Company Continental Airlines de Mexico, S.A. Continental Airlines Domain Name Limited Continental Airlines Finance Trust II Continental Airlines, Inc. Supplemental Retirement Plan for Pilots Trust Agreement Continental Airlines Purchasing Holdings LLC Continental Airlines Purchasing Services LLC Continental Express, Inc. Presidents Club of Guam, Inc. Four Star Insurance Company, Ltd. UAL Benefits Management, Inc. United Airlines, Inc. (the original United Airlines) Covia LLC Mileage Plus Holdings, LLC MPH I, Inc. Mileage Plus Marketing, Inc. Mileage Plus, Inc. United Aviation Fuels Corporation United Cogen, Inc. United Vacations, Inc. Development Early in February 2008, UAL Corporation and Continental Airlines began advanced stages of merger negotiations and were expected to announce their decision in the immediate aftermath of a definitive merger agreement between rival Delta Air Lines and Northwest Airlines. The timing of the events was notable because Northwest's golden shares in Continental (that