Abstract: Novel riser reactor design with associated multiple feed inlet means for contacting regenerated catalyst particles with low quality naphtha, C.sub.5 minus wet gas product of hydrocarbon conversion and a residual oil feed comprising components boiling above about 1025.degree. F. and comprising metal contaminants. Low quality naphtha from thermal cracking is charged either separately or in admixture with C.sub.5 and lower boiling wet gas product of hydrocarbon conversion to the bottom portion of the riser conversion zone for contact with freshly regenerated zeolite cracking catalyst. The vaporous material thus charged conveys the regenerated catalyst at an acceptable velocity to an expanded section of the riser wherein residual oil is charged by a plurality of nozzle means penetrating the wall of the riser in the transition section to the expander user section.