a process is provided for the desulfurization of residual oil by separating the residual oil into a first and a second fraction ; reacting the first fraction with hydrogen over a hydrodesulfurization catalyst in a first reaction zone at hydrodesulfurization conditions such that a liquid effluent of lower sulfur content than the residual oil is obtained ; combining the hydrodesulfurization liquid effluent with the second residual oil fraction ; and reacting the resultant mixture over a hydrogenation / dehydrogenation catalyst in a second reaction zone at hydrogen transfer conditions . this process provides for desulfurization of residual oils at lower hydrogen consumptions than conventional processes .