Two types of deactivation functions are usually employed when modelling catalytic cracking: the time-based models and the coke-on-catalyst models. In this paper, a comparison is made between these two types of deactivation functions in the simulation of an industrial UOP fluid catalytic cracking (FCC) unit with high-efficiency regenerator. For this purpose, a FCC mathematical dynamic model, previously presented and validated, is used. The dynamic responses to perturbations of +10% increase in the combustor air mass flowrate and +5% in the feedstock flow, were studied. The results for these perturbations show that the slight differences observed were due to the fact that the coke-on-catalyst approach takes into account the coke content present at the riser inlet. (C) 2012 Elsevier Ltd. All rights reserved.