In industrial fluid cokers, the feedstock, consisting of heavy bituminous hydrocarbons, is atomized with steam and injected into the hot fluidized bed of coke. Good and uniform contact of the liquid droplets with the solid particles is required to provide heat for the cracking reactions while mass transfer effects are minimized. Experiments in a pilot plant coker have suggested that the initial particle/liquid mixing, in the spray jet, is rather poor. Experiments in a X-ray scanner showed that liquid droplets and entrained particles accumulate just below the tip of the jet plume. To illustrate the importance of the initial liquid-solid mixing, a simple model has been proposed to predict its effect on coker yields. An experimental technique was developed to quantitatively determine the quality of mixing with current nozzle technology and a new enhanced solids entrainment (ESE) device. The model has been used in combination with the experimental results to show the effect of ESE on product yields. The ESE nozzle has been shown to greatly improve liquid/solid mixing by increasing the amount of wetted solids and achieving a more uniform initial liquid/solid mix. The model suggests that ESE will improve liquid yield by up to 0.6 wt % and reduce the coke yield by up to 2 wt %.