An apparatus and method for processing different feeds in a fluid catalytic cracking unit are disclosed which result in improved yields of C.sub.3, C.sub.4 and gasoline range hydrocarbons as compared to conventional systems. The process comprises injecting a main hydrocarbon feed into a catalyst-containing riser reactor through a plurality of main feed injectors, and injecting a light hydrocarbon feed into the riser reactor at a location upstream from the main feed injectors and downstream from a control valve such as a regenerated catalyst slide valve, the light feed being injected in a region having a high density of catalyst particles. The light feed is injected in a dispersed way such the amount of feed injected corresponds to the density of catalyst particles at that particular point, with greater amounts of feed being injected at locations having a large number of catalyst particles. Also, a heavy hydrocarbon feed or a heavy recycle stream from the same FCC unit can be injected at the same elevation as the main feed injectors but through separate injectors.