Simulated distillation data of distillates produced by hydroconversion of a vacuum residue have been described as a two-component cumulative normal distribution function. The influence of catalyst addition upon calculated parameters of the model indicates that distillate fraction is produced through a consecutive mechanism. A modified three-component model has then been applied. It reveals that catalyst limits the extent of the first bond cleavage step and reduces the yield of light distillate. Furthermore, the distribution of hydrogen consumption is strongly affected by catalyst addition, which favors hydrogen incorporation in distillate.