A relationship is developed for the change in local effective diffusivity with coking using the models available for effective diffusivity. When this relationship is combined with the earlier multilayer kinetic model, the local effective diffusivity becomes dependent solely on the fraction of catalyst deactivated. Experimental procedures developed determine the relationship for the local effective diffusivity. These results provide a framework for a consistent and systematic treatment of the complex deactivation-diffusion problem caused by coking and coke growth. Unique aspects of coking are accounted for through the fraction of catalyst deactivated, which is the basic quantity for catalytic activity, rather than the coke content.