A kinetic model for hydrocracking a real vacuum gas oil at 120 bar and 400 degrees C in a semi-batch reactor has been constructed based on analysis results from two dimensional gas chromatography (GC x GC). The model has 217 pseudo-component lumps classified by carbon number and hydrocarbon family. Hydrogenation and cracking reactions are included separately and product distributions are generated using a probabilistic approach. Mass transfer resistances and vapour-liquid equilibrium are also accounted for. 17 parameters were estimated and the resulting model is able to fit the experimental data quite well. It was found that it is important to consider the average molecular structure within each lump. To this end, the non-reactivity of components within the paraffin lumps is taken into account in the probability matrix. A parameter has been included for the number of branches removed from the aromatics and naphthenes and it was also necessary to separate the aromatics and naphthenes into mono-ringed and multi-ringed lumps. This many lumped model allows us to approach the results found in studies with model molecules. (C) 2015 Elsevier B.V. All rights reserved.