Abstract: A process and apparatus for the supercritical water oxidation of organic waste materials which avoids or at least substantially reduces the corrosion and solids deposition problems associated with prior art techniques and which provides for efficient heating of the waste material to reaction conditions. Externally heated supercritical water is fed to a compound platelet tube reactor. The compound reactor includes a reaction zone and inner (smaller) and outer (larger) concentric platelet tubes supported concentrically within a shell. The water fed to the reactor both protectively coats surfaces of the inner and outer platelet tubes facing the reaction zone and heats the waste stream to oxidation reaction conditions. Higher reaction temperatures can be used as compared to prior art processes, which significantly improves the reaction rate and permits smaller reactors to be used.