A control system for automatic operation of a fluid catalytic cracking unit is shown. The control system includes a reactor severity control device operable to modulate a temperature affecting volume gain within the fluid catalytic cracking unit and a controller. The controller includes a processing circuit configured to calculate the volume gain within the fluid catalytic cracking unit by comparing a volume based on one or more input oil feeds to the fluid catalytic cracking unit to a volume of one or more output oil products of the fluid catalytic cracking unit. The processing circuit is further configured to use a neural network model to generate a target severity predicted to optimize the volume gain within the fluid catalytic cracking unit. The processing circuit is further configured to operate the reactor severity control device using the target severity to modulate the temperature affecting the volume gain within the fluid catalytic cracking unit.