Simulated distillation, commonly applied to the characterization of complex products issued from the conversion of heavy petroleum fractions, provides information concerning the yield of distinct classes of distillable products. A simple modeling of simulated distillation data has been applied to several distillates obtained by hydroconversion of a vacuum residue. This model gives access to characteristic parameters which allows a description of this complex mixture in terms of two distinguishable components. The lighter one is produced through two simultaneous mechanisms, involving the rupture of substituted carbon positions and a symmetrical cleavage of the resulting molecules. The remaining component is representative of the initial feed and is preserved in a slightly modified state up to high level of conversion.