The phase behavior of the micellar solutions of styrene stabilized by sodium dodecyl sulfate (SDS) in the presence of cosolvent such as I-pentanol (POL), butyl acrylate (BA) and dodecyl methacrylate (DMA) was investigated. At a relatively low level of POL the spontaneous emulsification of styrene (St) appears. The addition of excessive POL, however, promotes the fort-nation of gel-like and milky emulsion products. The phase behavior upon the addition of alcohols may be the result of two competing factors: the stabilizing effect of micelles due to the micellization of alcohols with interfacial droplet layer versus the destabilizing effect resulting from transformation of isotropic droplets to anisotropic ones and disruptive change of the structure of water. The synergistic effect of BA increases with increasing SDS concentration. The poisoning effect of DMA on the colloidal parameters results from the depressed water solubility of reactants, increased hydrophobicity of amphiphile system, accumulation of monomer and additive in the droplet core and swelling effect. The size of polymer particles is independent of the initial droplet size. The final monomer conversion decreases with increasing concentration of POL or DMA and aging time of the monomeric emulsion. The broad droplet size distribution, however, excludes the scenario that nucleation takes place primarily in the microdroplets or the aqueous phase (homogeneous nucleation). The mixed mode of particle nucleation (monomer droplet nucleation and micellar nucleation or homogeneous nucleation) and depressed transfer of monomer from the highly monomer-swollen particles to the reaction loci are postulated to govern the kinetic and colloidal parameters of the emulsion polymerization of St with BA or DMA.