Ameren is a public utility holding company. Through its subsidiary, Union Electric Company, the company operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Through its subsidiary, Ameren Illinois Company, the company operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Through its Ameren Transmission Company of Illinois subsidiary, the company operates a Federal Energy Regulatory Commission rate-regulated electric transmission business. The company also has other subsidiaries that conduct other activities, such as providing shared services.

American Electric Power Company is a public utility holding company. The public utility subsidiaries of the company provide electric service, consisting of generation, transmission and distribution, on an integrated basis to their retail customers. The service areas of the company's public utility subsidiaries cover portions of the states of Arkansas, Indiana, Kentucky, Louisiana, Michigan, Ohio, Oklahoma, Tennessee, Texas, Virginia and West Virginia. Transmission networks are interconnected with distribution facilities in the territories served. The company's service company subsidiary provides accounting, administrative, information systems, engineering, financial, legal, maintenance and other services.

Black Hills is a utility holding company, which operates in four segments: Electric Utilities, which generates, transmits and distributes electricity to electric utility customers in Colorado, Montana, South Dakota and Wyoming; Gas Utilities, which serves natural gas utility customers in Arkansas, Colorado, Iowa, Kansas, Nebraska, and Wyoming; Power Generation, which produces electric power from its wind, natural gas and coal-fired generating plants and sells the electric capacity and energy primarily to its utilities under long-term contracts; and Mining, which produces coal at its mine near Gillette, WY, and sells it under long-term contracts to mine-mouth electric generation facilities.

Otter Tail is a holding company. Through its subsidiaries, the company's reporting segments include: electric, which includes the production, transmission, distribution and sale of electric energy in Minnesota, North Dakota and South Dakota by the company's subsidiary, Otter Tail Power Company; manufacturing, which consists of businesses engaged in the contract machining, metal parts stamping, fabrication and painting, and production of plastic thermoformed horticultural containers, life science and industrial packaging, and material handling components; and plastics, which consists of businesses producing polyvinyl chloride pipe at plants in North Dakota and Arizona.

Xcel Energy is a regulated electric and natural gas delivery company which serves customers in mid-western and western states, including portions of Colorado, Michigan, Minnesota, New Mexico, North Dakota, South Dakota, Texas and Wisconsin. The company's reportable segments include: regulated electric utility, which generates, transmits and distributes electricity in Minnesota, Wisconsin, Michigan, North Dakota, South Dakota, Colorado, Texas and New Mexico; regulated natural gas utility, which transports, stores and distributes natural gas primarily in portions of Minnesota, Wisconsin, North Dakota, Michigan and Colorado; and other, which includes steam revenue and appliance repair services.