UNS Energy Corporation, formerly UniSource Energy Corporation, is a holding company. The Company owns the outstanding common stock of Tucson Electric Power Company (TEP), UniSource Energy Services, Inc. (UES), UniSource Energy Development Company (UED), and Millennium Energy Holdings, Inc. (Millennium). It operates in three segments: TEP, UNS Gas, Inc. (UNS Gas) and UNS Electric, Inc. (UNS Electric). TEP is an electric utility serving the community of Tucson, Arizona. UNS Gas is a gas distribution company serving approximately 148,000 retail customers in Mohave, Yavapai, Coconino, and Navajo counties in northern Arizona, as well as Santa Cruz County in southeastern Arizona. UNS Electric is a vertically integrated electric utility company serving approximately 91,000 retail customers in Mohave and Santa Cruz counties. In July 2011, UNS Electric purchased the Black Mountain Generating Station (BMGS) from UED.