Petroleum residues are reduced in sulfur content by intimately contacting one volume of petroleum residue with at least 0.25 volume of alkali metal sulfide hydrate melt, or alkali metal hydroxide hydrate melt or mixtures thereof, within a closed system, at a temperature between 120.degree. C. and 325.degree. C., for from 3 to 60 minutes, thereafter separating de-sulfured petroleum residue from said alkali metal sulfide hydrate melt by a hot liquid-liquid separation, thereafter utilizing said separated alkali metal sulfide hydrate melt to de-sulfur additional petroleum residue.