Three types of tubular filters, i.e. 13 μm slots, 4 μm circular pores and 0.45 μm ceramic membranes, and 13 μm flat sheet slots were used to challenge 1000 ppm oil in water emulsion, the test liquid. The rejection of oil drops by pore size was also evaluated by incorporating a 17 mm pitch helix within the tubular slots and circular pore filters. The experimental data were analysed using filtration models. The model of droplet deformation indicates that poor rejection was caused by a low interfacial tension of emulsion system and that the oil drops could easily penetrate the filters even at low transmembrane pressure. However, the results of filtration models suggested that the use of slots was more likely to reduce the flux decay and the incorporation of a helix can greatly reduced the resistance to filtration.