Hydrocracking Fischer-Tropsch waxes is a catalytic process that occurs both in vapour phase and in liquid phase. In a previous model, worked out by the authors, only the presence of the vapour phase was considered. In this paper it is shown how to account for the vapour-liquid equilibrium (VLE). In particular, the method used to calculate the critical properties of heavy hydrocarbons and the computing procedure that allows one to introduce the VLE calculation into the reactor model are explained. The results show that by accounting for the VLE a better agreement between experimental data and model outputs can be achieved. This results from the improved ability of the model to take into account the effect of the H-2/waxes ratio both on the conversion and on the product distribution. (C) 2008 Elsevier Ltd. All rights reserved.