Exhibit 21 PRINCIPAL OPERATING SUBSIDIARIES FUEL RESOURCES INC. 1330 Post Oak Boulevard Houston, Texas 77056 R. Gerald Bennett President and Chief Executive Officer THE HOUSTON EXPLORATION COMPANY 1331 Lamar Houston, Texas 77010 James G. Floyd President and Chief Executive Officer GAS ENERGY INC. GAS ENERGY COGENERATION INC. 111 Livingston Street Brooklyn, New York 11201 David S. Milne, Jr. President and Chief Executive Officer