The present study focuses on the contribution of surface roughness to properties of polyacrylonitrile (PAN) membranes and its fouling during ultrafiltration (UF) of used engine oil. Nine membranes were cast using varying polymer concentration, molecular masses of hydrophilic additive polyethylene glycol (PEG), and concentration of PEG. Surface roughness decreased from 35 to 10nm with polymer concentration in the range 0.01-0.15g/g (1-15wt%). Surface roughness increased from 8 to 42nm as the molecular mass of PEG increased from 200 to 20 000g/mol. Increasing concentration of PEG from 0.5 to 0.12g/g (5 to 12wt%) increased the surface roughness from 11 to 26nm. Three membranes were identified as having permeate flux above 45 L/m(2)h and oil rejection beyond 90%. The membrane hydrophilically modified by 0.08g/g (8wt%) PEG 400 showed the best antifouling performance. The flux decline ratio for this membrane was the lowest between 10-20% and the flux recovery ratio was above 90% for oil concentrations between 100-1000mg/L at 276kPa transmembrane pressure (TMP). Permeate concentration was between 2-12mg/L (well within permissible levels) corresponding to oil concentrations from 100-1000mg/L in the feed at the same TMP. Permeation of oil is lower (hence higher rejection) at higher feed concentrations, indicating the agglomeration of oil in the retentate.