Xcel Energy Inc. is a holding company with subsidiaries engaged primarily in the utility business. Through its four regulated utility subsidiaries Northern States Power Company - Minnesota, NSP-Wisconsin, Public Service Company of Colorado and Southwestern Public Service Co. the company serves electricity customers and natural gas customers. Along with WYCO Development LLC and West Gas Inter State Inc., these companies comprise the regulated utility operations. Xcel Energy's operating utilities are engaged in the generation, purchase, transmission, distribution and sale of electricity in the U.S. The utilities generate electricity using coal, nuclear, hydro, wind and solar energy. Except SPS, the company's remaining utilities also purchase, transport, distribute and sell natural gas to retail customers, as well as transport customer-owned natural gas. Xcel Energy is undertaking initiatives to produce and deliver clean energy to customers.