A consistent high quality coke is produced by feeding a balancing stream comprising hydrocarbons to a delayed coking drum in addition to the heavy hydrocarbonaceous coker feedstock. The process of this invention reduces the contaminant content of coke by coking contaminant-containing residua and a reduced contaminant hydrocarbon balancing stream. Preferably, the balancing stream is a contaminant diluent, such as unreduced crude. The balancing stream may be a crude which is different from the base crude processed in the refinery crude tower and is preferably selected as a sulfur and/or metals diluent having a lower concentration of sulfur-containing or metal-containing compounds than the heavy coker feedstock.