Silica nanoparticles have been synthesized in AOT/decane/ammorium hydroxide reverse microemulsions via-base-catalyzed hydrolysis of tetraethoxysilano (TEOS). The effect of inter-micellar exchange has been investigated by conducting the synthesis experiments in the presence of benzyl alcohol (BA), an additive which is known to act as a cosurfactant at the water/oil interface, increasing the inter-micellar exchange rates. Larger, more monodisperse particles are formed at higher benzyl alcohol concentrations. Furthermore, the presence of high concentrations of benzyl alcohol (BA/AOT molar ratios larger than 1.5) promotes phase separation, probably due to the combined effects of the high benzyl alcohol content and the presence of ethanol (a product of the TEOS hydrolysis reaction). The effects of benzyl alcohol concentration on particle size and size distribution have been attributed to the inhibition of nucleation by fast rearrangement of hydrolyzed TEOS species.