A study has been made of the oxidation of sulphur compounds in a diesel fraction and also sulphoxide concentrate by hydrogen peroxide to sulphones under foam-emulsion conditions in the presence of compounds of variable-valency metals. It has been established that organic derivatives of molybdenum and vanadium are effective catalysts for the oxidation of sulphides to sulphones. The best results were obtained in the presence of water-soluble molybdenum ethylene glycolate. The advantage of this catalyst is the absence of corrosion of the equipment and the possibility of its repeated use in a closed cycle.