Hybrid submicron emulsions were prepared using an energy-efficient phase inversion emulsification technique. Polyisobutene was dissolved in a vinyl monomer (styrene or methyl methacrylate), and a transitional phase inversion was induced by using a combination of hydrophilic and hydrophobic polyoxyethylene nonylphenyl ether surfactants. An important result was that the minimum size of drops was obtained in the vicinity of a locus of transitional inversion, but prior to that inversion. Increasing the monomer content in the polymer solution increased the hydrophilic-lipophilic balance at phase inversion until eventually no inversion could occur for the higher monomer content. The emulsions with average diameter of about 500 nm were subjected to polymerization. The miniemulsions prepared with a high concentration of monomer produced formulations close to those of optimum formulation, at which the interfacial tension is very low, and underwent massive coagulation during polymerizations. Miniemulsions prepared with low monomer content were sufficiently distant from the corresponding phase inversion locus and showed a good stability in the course of polymerization, leading to formation of hybrid polymer particles.