The influence of composition and preparation variables on the properties of W/O highly concentrated emulsions obtained in the system Span 80/oil/water was studied. Emulsions prepared with decane, dodecane and hexadecane were analysed. Stability of emulsions was found to depend on the oil as follows: stability of hexadecane emulsions > dodecane > decane. It was attributed to the lower solubility of water in the oil with longer chain. Experimental design tools were used to study the influence of composition and preparation variables and scale-up on the droplet size and polydispersity of emulsions formed. The most important factor was found to be the surfactant-oil ratio, SO, as more surfactant could stabilize more interface, but other preparation variables, like mixing rate, omega, were also found to influence the droplet size and polydispersity. The proper scale-up variables were found not to correspond to the dimensionless variables commonly used in scale-up studies, but total addition time, t(t), and angular mixing velocity, omega, seemed to be the proper ones. (C) 2010 Elsevier Inc. All rights reserved.