Catalyst deactivation by foulant deposition arises from interactions of the accumulating deposit with the geometry and void structure of particle porosity. Simple approaches involving a wedge-layering deposition in a parallel bundle of pores allow activity loss by surface coverage and pore plugging. More complex models use coking rates related to local concentration in bundles of randomly corrugated pores or in interconnected arrays of pore segments forming stochastic pore networks. Examples and illustrations are presented for cumene cracking on a supported zeolite catalyst. The optimal design of support pore structure to resist deactivation by coking is briefly discussed.