A method and apparatus is disclosed for oxidation of aqueous mixtures of organic material, including toxic material in the presence of inorganic materials, by reaction of said material with water and oxygen at supercritical conditions. Oxygen and the aqueous mixture are separately pressurized to greater than about 218 atmospheres, combined to form a reaction mixture and then directed through a tubular reactor having a substantially constant internal diameter. The velocity of the reaction mixture is sufficient to prevent settling of a substantial portion of solids initially present in the reaction mixture and of solids which form during passage through the reactor. The mixture is heated to temperature above about 374° C. in the tubular reactor. A substantial portion of the organic material in the reaction mixture is oxidized in the tubular reactor to thereby form an effluent mixture. Inorganic salts in the effluenet mixture, which are insoluble at conditions of supercritical temperature and pressure for water, are dissolved in a liquid water phase during cooldown of the effluent mixture at an outlet end of the reactor. Inorganic solids that are not soluble in the effluent mixture can be separated from a substantial portion of the effluent mixture by filtration prior to subsequent depressurization of the effluent mixture.