In this work the supercritical fluid extraction of grape seed oil in a semi-continuous unit has been modelled and discussed in detail. The model embodies the concept of broken plus intact cells, and assumes series mass transfer from intact to broken cells, and then to the fluid phase. The numerical solution has been accomplished by the method of lines using finite differences with upwind flow correction. Experimental extraction curves for both untreated seed and enzymatically pre-treated seed have been modelled in order to evaluate the performance of the model in terms of correlation capability and physical meaning of the parameters. The extraction curves for untreated and treated seed have been accurately represented with average deviations between 2.30 and 7.25%. The model parameters that are intimately related with the internal structure of the seed are the grinding efficiency (or fraction of broken cells) and the internal mass transfer coefficient. Both parameters have been optimised and attained physically sound values, in view of the fact they increased after the enzymatic pre-treatment, and obeyed simple restrictions imposed. The model has been able to generate coherent concentration profiles in the bed and elution curves as well. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.