The sonochemical oil-in-water miniemulsion polymerization of n-butyl methacrylate (BMA) has been studied in mixtures with a range of aliphatic and aromatic hydrocarbon liquids under ambient conditions. Measurements of monomer conversion percentage and molecular weights of the BMA polymers were performed to investigate the effect of the various organic liquids on the kinetics of the polymerization process and on the properties of the resultant polymers. Both the rates of polymerization and the molecular weights of the polymers formed were found to be dependent on the amount and type of the organic liquid present in the emulsion. The experimental results revealed that when the organic liquids were aliphatic, there were no significant changes in the rates of BMA polymerization whereas when the organic liquids were aromatic, the rates of polymerization were greatly reduced. Molecular weight data of the BMA polymers showed that in the presence of an organic liquid, the size of the polymer significantly decreased. The results have been interpreted in terms of the formation of a radical complex between the propagating radical and the organic liquid in the oil mixture, as well as chain transfer reactions that affect the kinetics of the polymerization process.