The Use of a submerged membrane bioreactor for the treatment of industrial oil contaminated wastewater was investigated using microfiltration hollow fibre membranes. The membrane bioreactor worked with a hydrocarbon concentration ranging from 600 to 1500 mg/L, in a sub-critical flux regime. The sludge concentration ranged From 14 g/L to 28 g/L During the long-term bioreactor test, three further different membrane Modules were tested in order to assess their critical flux in comparable conditions. The membranes investigated were different in materials. pore structure and size. The membranes with larger pore size showed a higher tendency to irreversible fouling. The MBR was able to treat wastewater with hi-h removal efficiency (about 98%), low hydraulic retention time (about 10 h) and high biomass concentration.