Abstract: A method for catalytically cracking different fractions of crude oil with a zeolite containing catalyst in separate riser regeneration zone followed by sequential regeneration of catalyst particles in separate riser regeneration zones is described wherein the hydrocarbon vapor-catalyst suspension of hydrocarbon conversion is discharged downwardly from a half circle centrifugal separation conduit comprising the riser upper discharge section, second stage riser regeneration of catalyst is discharged downwardly from a half circle centrifugal separation section into the top of a high temperature catalyst recovery zone provided with cyclone separation zones external thereto. The first stage upflow riser regeneration zone is effected with oxygen lean gas and steam in an amount equal to, more or less, than the oxygen containing gas whereby the regeneration temperature is restricted from exceeding a desired upper temperature limit with or without promoting the water gas shift reaction.