A mathematical model, previously developed to describe deactivation by metal deposition, has been applied to catalyst with macro-, micro- and random pore structures. Simulation results showed that effectiveness factor reduces progressively with the increasing age of the catalyst. For the macropore system, catalyst lifetime was found to be over I year and it is the highest in comparison with both micropore and random pore models. It was revealed that a pore structure in which the pore diameter is enlarged increases hydrodemetallization activity and will be very effective for improving metal resistance because pore-mouth plugging can be curtailed. Predicted catalyst lifetimes matched plant data very closely. The need to develop catalysts of optimum pore structure to achieve desirable goals has been validated. (c) 2005 Elsevier B.V. All rights reserved.