The invention relates to an integrated, continuous process for the removal of organically bound sulfur (e.g., mercaptans, sulfides and thiophenes) comprising the steps of contacting a heavy oil, sodium hydroxide, hydrogen and water at a temperature of from about 380.degree. C. to 450.degree. C. to partially desulfurize the heavy oil and to form sodium sulfide, contacting said sodium sulfide with a transition metal in water to form a transition metal sulfide, sodium hydroxide and hydrogen. The sodium hydroxide is recirculated and the transition metal sulfide is removed. The partially desulfurized, dewatered heavy oil is treated with sodium metal under desulfurizing conditions, typically at a temperature of from about 340.degree. C. to about 450.degree. C., under a hydrogen pressure of at least about 50 psi to essentially desulfurize the oil, and form sodium sulfide. Optionally, the sodium salt generated can be regenerated to sodium metal using regeneration technology. The process advantageously produces essentially sulfur-free product oils having reduced nitrogen, oxygen and metals contents and reduced viscosity, density, molecular weight and heavy ends.