A Monte Carlo Model was developed to simulate the free-radical chlorination of n-alkanes by which polychlorinated alkane mixtures are produced. The model parameters were the relative reactivity of the hydrogen atoms on the alkane chain to chlorine free-radical substitution. The values of the parameters were determined by free-radical chlorination experiments; by interpolation of data from these experiments or from data in the literature. The result of the model is a complete characterization of the molecular composition of PCA mixtures of any carbon chain length and degree of chlorination. Properties of modeled PCA mixtures were in good agreement with properties of real PCA mixtures. This model represents the first published attempt to characterize polychlorinated alkane mixtures.