Abstract: A wet oxidation apparatus comprising a reactor vessel, means for continuously introducing combustible material, water, and oxygen containing gas, into the reactor; the heat of combustion in the reactor being sufficient to evaporate the water supplied to said reactor, means controlling the quantity of water fed to the reactor, thereby maintaining the liquid level in the reactor, and a gas and water vapor outlet for the reactor; gas and water vapor discharging from the reactor being passed through a turbine or similar device to produce mechanical power. The air supplied to the reactor is controlled to be insufficient to oxidize all of the fuel supplied to the reactor, or alternately, the reactor is operated in a way to enrich the gas and water vapor stream discharging from the reactor with organic matter, said enriched stream being subjected to vapor phase oxidation creating a superheated stream improving the efficiency of the power producing cycle.