The desulfurization of fossil fuels is effected by the combination of fossil fuels with an aqueous mixture of hydroperoxide and quaternary ammonium fluoride phase transfer catalyst, the mixture then subjected to ultrasound to oxidize sulfur compounds present in the fuels. The polar oxidized species are removed via extraction. Another aspect is a portable, continuous ultrasound assisted desulfurization device having a sonoreactor for subjecting mixtures of fossil fuels to sonication to effect removal of sulfur containing compounds.