A method of predicting the tendency of a heavy oil feed to generate coke deposits in the FCC riser under a given set of operating parameters in the unit; thus, by utilizing operating parameters appropriate to the feed, the formation of coke deposits in the riser may be minimized. The margin between the theoretical dew point of the hydrocarbon feed established from unit operating parameters and the theoretical mix zone temperature in the feed injection zone of the unit is developed by applying a regression-derived linear model from multiple rigorous model runs. The mix zone of the unit is then operated at a temperature which reduces the level of riser coking predicted from this ascertainable margin or, at least, maintains it within levels which are predictable and acceptable.