A microporous hydrophobic membrane allows the permeation of an oil phase at almost zero pressure and retains the water. The separation of dilute oil-in-water mixtures using flat sheet hydrophobic PVDF membranes has been investigated using an unstirred laboratory scale semi-batch experimental system operated at 40 degrees C. The flat sheet membranes were prepared in the laboratory by an immersion precipitation method and were characterised in terms of a mean pore radius, porosity and breakthrough pressure. The oil-in-water mixture contains 1% kerosene in distilled water. The experimental work essentially entails the study of the effects of various system parameters on the oil/water separation characteristics. In particular, the effects of feed flow rate, the operating pressure and pore size and porosity of the membrane were studied. The experimental results can be predicted reasonably well using the Hagen-Poiseuille equation at a high vertical velocity and the percentage of oil removed can be achieved as high as 77% under normal experimental conditions.