In this paper the impact design has on the control of a fluidized catalytic cracker (FCC) is explored. The available control options depend strongly on the availability of manipulated variables as well as on downstream equipment. Also of importance is the range in which each variable can be manipulated. An important distinction is made between the total number of manipulated variables and the effective degrees of freedom for control, especially of the product specification vector Y-p. Control both in complete CO combustion when there is no CO boiler available and in partial combustion when a boiler is present is analyzed. The fast manipulated variables of air flowrate, catalyst circulation rate, feed preheat, and catalyst cooler heat removal rate are all considered. It is shown that the sufficiency of a partial control structure changes when the operating conditions change and that it strongly depends on the control objectives. Also examined is the impact of catalyst activity.