The kinetic mechanisms of petroleum sulfoxide oxidation by hydrogen peroxide in the presence of molybdic and tungstic acid catalysts are studied. The reaction orders with respect to the reagents in the kinetic equation are determined. A scheme of catalytic peroxide oxidation of petroleum sulfoxides that explains the obtained experimental results is presented in a generalized form. Based on the kinetic data, it is shown that peroxy acids act as sulfoxide oxidants and the intermediate reaction products are most probably complexes of sulfoxide with peroxy acids present in the reverse emulsion shell.