Oil-in-water premix membrane emulsification was successfully carried out using various nickel sieves having rectangular (width < < length) or squared pores. The emulsification process was characterized using droplet Reynolds number (Re-d), droplet Weber number (We(d)) and dimensionless pressure (P-ratio). The inertial forces were found to be more important for sieves having rectangular pores that allow more chances for liquid-liquid interactions. Whereas, in case of sieves having squared pores spontaneous droplet break-up due to Laplace pressure differences may be more important. The curve between We(d) and P-ratio represents a change in the droplet break-up mechanism from spontaneous to shear based (extension) for each sieve (depending on ingoing droplet size) and between different sieves (in terms of efficient energy usage). Stacking sieves either on top of each other or at some distance was found to have no additional effect on droplet break-up compared to two separate passes. This illustrates the importance of matching the residence time between two passes with the interfacial dynamics of the surfactant system used. (C) 2013 Elsevier Ltd. All rights reserved.