EXHIBIT 21 SUBSIDIARIES OF NEW CENTURY ENERGIES, INC As of December 31, 1997 Subsidiary State of Incorporation 1. Public Service Company of Colorado Colorado 2. Southwestern Public Service Company New Mexico 3. Cheyenne Light, Fuel and Power Company Wyoming 4. WestGas InterState, Inc. Colorado 5. New Century Services, Inc. Delaware 6. NC Enterprises, Inc. Delaware SUBSIDIARIES OF PUBLIC SERVICE COMPANY OF COLORADO As of December 31, 1997 Subsidiary State of Incorporation 1. 1480 Welton, Inc. Colorado 2. PSR Investments, Inc. Colorado 3. PS Colorado Credit Corporation Colorado 4. Green and Clear Lakes Company New York 5. Fuel Resources Development Co. (a dissolved Colorado corporation) Colorado 6. New Century International, Inc. Delaware