The water solubility and thermal stability of sulfoxide concentrates obtained by oxidation of Arlan Crude Oil Diesel fuel cuts with hydrogen peroxide followed by separation of sulfuric acid were investigated. A dependence was found between the cutpoints and water solubility of the sulfoxide concentrates obtained from these cuts. The effect of the degree of oxidation of the sulfides and content of iron compounds in the feedstock on the quality of the sulfoxide concentrates was examined.