Atmos Energy (NYSE: ATO), heaquartered in Dallas, Texas, is the largest distributor of natural gas in the United States, serving 3.1 million customers nationwide. Atmos acquired TXU's natural gas and pipeline holdings in 2004. The company began as Energas in 1983, a spinoff of the natural gas distribution division of Pioneer Corporation. In 1988, the company changed its name to Atmos and began trading on the New York Stock Exchange.