A mathematical model for the computation of the molecular weight distribution (MWD) of the sol, the gel fraction, and the gel point in emulsion polymerization systems was developed. The model accounts for the compartmentalization of the free radicals in the reaction system and for the changes in the environment where the chain was growing. An improved numerical fractionation technique that allows a better description of the MWD of the sol was used. A parametric sensitivity analysis was carried out and a comparison between the batch and the semicontinuous processes is presented.