AbstractSchemes of high-temperature turbines operating on hydrogen-oxygen and methane-oxygen fuels, the design of an experimental prototype of such a turbine with a capacity of 100 kW, and the results of its testing are described. A combustion chamber for burning methane-oxygen fuel in steam was developed, manufactured, and tested in a laboratory test setup. A unit for additional gas superheating of the working fluid was designed, manufactured, and tested on the basis of the T-25-90-4PR-1 turbine at the cogeneration power plant TETs-16 of the branch of JSC Mosenergo. The experimental studies have demonstrated stable combustion of the methane-oxygen mixture in a steam environment and confirmed the serviceability of the technology for additional gas-fired superheating of the working fluid in a real thermal power plant. Temperature distributions in the metal of the flame tube and casing during start-up and under the design conditions were obtained. The technical characteristics of the high-temperature gas-steam-turbine unit and the classical K-300-23.5-3 version are compared. Unavailability of regulations required for the implementation of an unconventional project at a real thermal power plant is noted. The required technical basis was obtained, and the procedure for elaboration of a demonstration model of a high-temperature gas-steam turbine with a capacity of 25 MW at a temperature of 1000°C and a prototype of a power unit with a capacity of 300–500 MW for a pressure of 30 MPa at a temperature of 1250/1450°C was proposed.