Fluid coking with H.sub.2 S addition

In a fluid coking process comprising the steps of contacting a carbonaceous material having a Conradson carbon content of at least 5 weight percent with hot fluidized solids in a fluidized coking bed contained in a coking zone maintained in a fluidized state by the introduction of a fluidizing gas and operated at coking conditions, including a pressure ranging from about 0 to about 150 psig, to produce a vapor phase product and a solid carbonaceous material which deposits on said fluidized solids, the improvement which comprises introducing into said coking zone a fluidizing gas comprising from about 5 to about 40 mole percent of hydrogen sulfide, based on the total gas introduced into said coking zone.