The microfiltration of oil has been measured using a stirred cell fitted with Nuclepore filters with pore sizes of 2, 5, 8 and 10 mu m. These filters are produced by nuclear bombardment followed by chemical etching and have pores which pass directly through the filter from one side to the other. The oil emulsion drop size was in the range of 1-40 mu m and was stabilised using an aqueous solution of polyvinyl alcohol (PVA). The rejection of oil and the size distribution of the permeate were determined for transmembrane pressures varying from 400 to 3000 Pa. A simple theory based on interfacial tension, contact angle and pore size is described and the results compared with the experimental measurements. There is good agreement between the measured and predicted results for both the permeate size distribution and the oil rejection for the 2 mu m filter, but the model reliability decreased with increasing pore size.