. . . Exhibit 21 SUBSIDIARIES OF ATMOS ENERGY CORPORATION State of Percent of Name Incorporation Ownership ---- ------------- --------- ATMOS ENERGY HOLDINGS, INC. Delaware 100% MISSISSIPPI ENERGIES, INC. Mississippi 100% MISSISSIPPI WASTEWATER, INC. Mississippi 100% MISSISSIPPI WATER, INC. Mississippi 100% ATMOS ENERGY SERVICES, LLC Delaware 100% (a limited liability company) (wholly-owned by Atmos Energy Holdings, Inc.) EGASCO, LLC Texas 100% (a limited liability company) (wholly-owned by Atmos Energy Holdings, Inc.) ENERGAS ENERGY SERVICES TRUST Pennsylvania 100% (a business trust) (wholly-owned by Atmos Energy Services, LLC) UNITED CITIES PROPANE GAS, INC. Tennessee 100% (a wholly-owned subsidiary of Atmos Energy Holdings, Inc.) ENERMART ENERGY SERVICES TRUST (a business trust) Pennsylvania 100% (wholly-owned by Atmos Energy Holdings, Inc.) ATMOS ENERGY MARKETING, LLC Delaware 100% (a limited liability company) (wholly-owned by Atmos Energy Holdings, Inc.) ATMOS POWER SYSTEMS, INC. Georgia 100% (a wholly-owned subsidiary of Atmos Energy Holdings, Inc.) ATMOS PIPELINE AND STORAGE, LLC Delaware 100% (a limited liability company) (wholly-owned by Atmos Energy Holdings, Inc.) State of Percent of Name Incorporation Ownership ---- ------------- --------- UCG STORAGE, INC. Delaware 100% (wholly-owned by Atmos Pipeline and Storage, LLC) WKG STORAGE, INC. Delaware 100% (wholly-owned by Atmos Pipeline and Storage, LLC) ATMOS EXPLORATION AND PRODUCTION, INC. Delaware 100% (wholly-owned by Atmos Pipeline and Storage, LLC) TRANS LOUISIANA INDUSTRIAL GAS COMPANY, INC. Delaware 100% (wholly-owned by Atmos Energy Marketing, LLC) WOODWARD MARKETING, LLC Delaware 100% (a limited liability company) (wholly-owned by Atmos Energy Marketing, LLC) SOUTHERN RESOURCES, INC. Kentucky 100% (wholly-owned by Woodward Marketing, LLC) TRANS LOUISIANA GAS PIPELINE, INC. Louisiana 100% (wholly-owned by Atmos Pipeline and Storage, LLC) TRANS LOUISIANA GAS STORAGE, INC. Delaware 100% (wholly-owned by Atmos Pipeline and Storage, LLC) Effective October 1, 2003, Southern Resources, Inc. was merged with and into Woodward Marketing, L.L.C., Trans Louisiana Industrial Gas Company, Inc. was merged with and into Atmos Energy Marketing, LLC, Atmos Energy Marketing, LLC was merged with and into Woodward Marketing, L.L.C., and Woodward Marketing, L.L.C. was renamed Atmos Energy Marketing, LLC. Also, after its sale to a third party effective October 1, 2003, Mississippi Wastewater, Inc. is no longer a subsidiary of the Company.