Miniemulsion polymerizations have been carried out using only an oil-soluble initiator (lauroyl peroxide) as the cosurfactant. Diffusional instability was reduced to the point where nucleation in the monomer droplets and polymerization could be carried out before significant diffusional degradation of the droplets took place. The polymerization behavior was that expected in miniemulsion polymerization with more conventional cosurfactants.