United Continental Holdings, Inc. , is a publicly traded airline holding company, incorporated in Delaware with headquarters in the United Building in Chicago, Illinois. UCH owns and operates United Airlines, Inc. and Continental Airlines, Inc. both of which use the trade name United Airlines. The company is the successor of UAL Corporation, which agreed to change its name to United Continental Holdings in May 2010, when a merger agreement was reached between the airlines. Its stock trades under the UAL symbol. To effect the merger, 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. United, when it is completely combined, will be the world's largest airline, as measured by revenue passenger miles. United is a founding member of the Star Alliance.