A mathematical model for the study of reaction kinetics and molecular weight distributions in miniemulsion polymerization systems with oil-soluble initiators is presented. The mathematical model allows the computation of the evolution of the complete molecular weight distribution with chain lengths of up to 10(5) mers in miniemulsion polymerization by direct integration in reasonable computational time. Also, no restriction in the kinetic regime is needed, as the model is able to represent both compartmentalized and pseud-bulk systems. The model was validated with experimental results for methyl methacrylate and styrene homopolymerizations, with two different oil-soluble initiators, and adequately represented both the kinetics and molecular weight distributions of these systems. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2128-2140, 2017