Abstract: A fluid coking process is operated in a fluidized bed coking reactor in which a plurality of heavy oil inlet nozzles are arranged in a number of rings around the periphery of the dense bed reaction section at vertically spaced elevations. A heavy oil feed is injected with atomization steam through the nozzles into the fluidized. bed, operating at a lower steam-to-oil ratio for the upper ring or rings of nozzles than for the lower ring or rings.