Present invention relates to a novel process for upgrading a residual hydrocarbon oil feedstock having a significant amount of Conradson Carbon Residue (concarbon), metals, especially vanadium and nickel, asphaltenes, sulfur impurities and nitrogen to a lighter more valuable hydrocarbon products by reducing or minimizing coke formation and by injecting fine droplets of oil soluble organo-metallic compounds at multiple elevations of the riser with varying dosing rates.