Modified ultrafiltration membranes are prepared and tested in treating oily aqueous solutions. Polyethersulfone ultrafiltration membranes are modified utilizing surface modifying macromolecules. Casting solutions are prepared containing various amounts of surface modifying macromolecules as additives. Ultrafiltration membranes are prepared using the phase inversion technique. The performance of the modified and control membranes is subsequently evaluated in treating oil/water emulsions as well as pure water. The membrane performance is characterized in terms of pure water permeation rates (PWP), product rate when oil/water are used as feed (PR), as well as oil separation. The resistance model is used to further quantify the effect of the surface modifying molecules on the gel layer resistance of the membranes under investigation. It is found that the modified polyethersulfone membranes have a superior performance, reflected in their higher flux when treating oil/water emulsions, than the control unmodified membranes. The oil gel layer resistance of the membranes decreased with an increase in the surface modifying macromolecules.