Xcel Energy Inc. directly owns six utility subsidiaries that serve electric and natural gas customers in 12 states. These six utility subsidiaries are Northern States Power Co., Northern States Power Co., Public Service Co. of Colorado, Southwestern Public Service Co., Black Mountain Gas Co. and Cheyenne Light, Fuel and Power Co. Xcel Energy's regulated businesses also include Viking Gas Transmission Co. and WestGas InterState, Inc., both interstate natural gas pipeline companies. In addition, Xcel Energy owns or has an interest in a number of non-regulated businesses, the largest of which is NRG Energy, Inc. (NRG), a power producer. In addition to NRG, Xcel Energy's non-regulated subsidiaries include Utility Engineering, Seren Innovations, Inc., e prime inc., Planergy International, Inc., Eloigne Co. and Xcel Energy International.