Cloud Peak Energy owns and operates three surface coal mines in the Powder River Basin of Montana and Wyoming. One of the largest producers of coal in the US, it sells mainly to utilities and industrial customers and accounts for about 3% of the electricity generated in the US. Formerly part of Rio Tinto, it sells about 60 million tons of coal annually and controls almost 1.1 billion tons in proved and probable reserves. Cloud Peak supplies coal to more than 45 domestic and foreign electric utilities. The company was formed in 1993 as Kennecott Coal.