BACKGROUND: Produced water is generated in huge volumes from oil and gas production facilities. Different alternatives including physical, chemical, and biological methods can be applied for the treatment of produced waters. In this study, different pre-treatment alternatives used before a final nanofiltration and reverse osmosis membrane system were evaluated. A membrane bioreactor and pressurized microfiltration and ultrafiltration systems were used in the pre-treatment stage. RESULTS: According to the results, the highest flux was obtained by the combination of ultrafiltration/microfiltration and nanofiltration; whereas, the maximum removal efficiencies for conductivity and chemical oxygen demand were obtained by the combination of membrane bioreactor and reverse osmosis systems. CONCLUSION: The results of this study show that the emphasis should be placed on applying the right combination of membrane treatment processes instead of focusing only on pre- or final treatment units. (C) 2012 Society of Chemical Industry