Abstract: A multiple-stage catalytic conversion system in which a hydrocarbonaceous charge stock is reacted in a plurality of catalytic reaction zones, through all of which the catalyst particles flow downwardly via gravity-flow. The charge stock, in the absence of added, or recycled hydrogen, is reacted in the last reaction zone, from which deactivated catalyst particles are withdrawn for regeneration. The reaction product effluent emanating therefrom is further reacted in an intermediate reaction zone. Additional reaction of the product effluent, from the intermediate zone, is effected in the first reaction zone, through which fresh, or regenerated catalyst particles are introduced into the system. The effluent from the first reaction zone is separated to recover the intended product. The system may comprise three or more reaction zones in side-by-side relationship, with the catalyst particles being transported from the lower end of one zone to the upper end of the next succeeding reaction zone.