San Antonio has a diversified economy, ranking 4th among Texas metropolitan areas and 38th in the United States. San Antonio’s economy is focused primarily within military, health care, government civil service, financial services, oil and gas and tourism sectors. Within the past twenty years, San Antonio has become a significant location for American-based call centers and has added a significant manufacturing sector centered around automobiles. San Antonio is home to six Fortune 500 companies: Valero Energy Corp, Tesoro Corp, USAA, Clear Channel Communications, NuStar Energy and CST Brands, Inc. H-E-B, the 19th largest private company in the United States is also headquartered in San Antonio. Other companies headquartered in San Antonio are: Bill Miller Bar-B-Q Enterprises, Carenet Healthcare Services, Eye Care Centers of America, Frost Bank, Harte-Hanks, Kinetic Concepts, NewTek, Rackspace, Taco Cabana and Whataburger. Other large companies that operate regional headquarters in the city include: Nationwide Mutual Insurance Company, Kohl’s, Allstate, Chase Bank, Philips, Wells Fargo, Toyota, Medtronic, Sysco, Caterpillar Inc., AT&T, West Corporation, Citigroup, Boeing, QVC, and Lockheed Martin.