An FCC process and apparatus is arranged to provide a low volume dilute disengagement zone in a reactor vessel and a quench zone immediately downstream of the reactor vessel. A vented riser that provides an open discharge of catalyst and gaseous products is directly discharged into a reactor vessel. The interior of the reactor vessel is arranged such that the outlet of the reactor riser is located close to and directed at the top of the reactor vessel. The reactor vessel operates with a dense bed of catalyst having an upper bed level that is only a short distance below the outlet of the reactor riser. The cyclone separators are located to the outside of the reactor riser and circulate catalyst back to the dense bed of the reactor section. The quenching takes place downstream of the cyclone separators.