From the viewpoint of utilizing energy most effectively, cogeneration plants in which gas turbines are the main power producers are being spotlighted due to their excellent overall thermal efficiency. To date, the excellent performance of the MF-111 gas turbine has been verified in more than 30 cogeneration plants. To meet a variety of needs, Mitsubishi Heavy Industries, Ltd. Developed the 25-35 MW class high-performance gas turbine MF-221. The performance and reliability of the prototype engine were verified in a full load shop test carried out in 1994.