Tokyo Electric Power Co Holdings, or TEPCO, is a holding company that, through its subsidiaries, supplies electric power to Tokyo's metropolitan area in Japan. TEPCO segments its business operations through subsidiaries that, manage fuel and thermal power generation, power transmission and distribution, and retail electricity sales. To produce electricity, the company controls a portfolio of hydroelectric, thermal, and nuclear power plants. TEPCO's thermal facilities, which utilize oil, natural gas, and coal fuel sources, account for the vast majority of its energy production. Almost all of Tokyo Electric Power's revenue is derived from the sale of electricity to primarily retail customers. The company serves the energy needs of a substantial portion of Japan's population.