Fouling of asymmetric, single tube ceramic membranes during ultrafiltration of Cold Lake heavy oil, is described by a pore restriction fouling model that predicts reduced permeate flux but increased asphaltene rejection with increased time-on-stream. Application of the model to experimental data showed that a 2nd-order rate of asphaltene adsorption/deposition within the membrane pores, described the data better than a Ist-order model. The asphaltene molecular radius, estimated as a parameter of the model, was in the range 3.8-14.2 nm, depending on the membrane pore diameter. These values are in good agreement with previously published estimates of asphaltene particle size, determined using : different experimental techniques.