A recyclable amphiphilic catalyst, which composed of peroxotungsten anion and quaternary ammonium cation assembled in the interface of the emulsion droplets, shows high selectivity and activity in the oxidation of sulfur-containing molecules to sulfones with hydrogen peroxide in diesel under mild reaction conditions. All the sulfur-containing molecules present in diesel can be completely oxidized into sulfones with -100% selectivity of sulfones in W/O (H2O2-in-diesel) emulsion system. The sulfones can be readily separated from the diesel, and the sulfur level of the desulfurized diesel can be lowered from about 500 ppm to below 1 ppm with about 98% yield of oil. In addition, the S-containing molecules in straight-run gas oil are also readily oxidized to their corresponding products in the OAV emulsion reaction medium. The S-level of oil layer of the oxidized oil was reduced to below 1 ppm from 312 ppm in the original straight-run gas oil with above 99% yield of oil. The amphiphilic catalysts serve as not only a catalyst but also an emulsifying agent to stabilize the emulsion droplets. The emulsion droplets are not only in the highly dispersed form but also behave like homogenous catalyst with high activity. The limitations due to interphase mass transport are greatly reduced in emulsion reaction medium. Moreover, the emulsion catalysts can be easily separated and recycled by demulsifying. (c) 2006 Elsevier B.V. All rights reserved.