The authors have evaluated the emulsification of oil of varying viscosities for concentrated o/w emulsions (>60%). Rushton type impellers and baffled mixing vessels were used. The emulsions were prepared in the transition regime (80 < Re < 200). It was found that, when the oil content increases, it is the emulsion viscosity that controls droplet size, regardless of the dispersed phase viscosity and hydrodynamics. The authors have followed an experimental procedure that allows for the scale-up of the results.