O A continuous method and apparatus for contact of olefin (1,47) with paraffin (7) in the presence of HF catalyst to produce alkylate in which about one half of the olefin feedstock (1,47) is passed to each of two riser reactors (11,45) with product effluent from both reactors entering a common settling vessel (15) with return (17) of settled HF catalyst proportioned between the two reactors (11,45) and the paraffin feedstock supported as fresh or alkylate fractionator side stream recycle (5) to one reactor and as reaction product recycle from the settler (15) to the other reactor (45).