Every day, about 100 million barrels of hazardous oily wastewater from oil and gas exploitation industry, called “Produced Water”, are discharged into environment around the world (Igunnu & Chen, 2014). Over time, stricter and more advanced regulations for discharging produced water have being passed. Concurrently, the potential of using produced water as fresh water is gaining more attention and interest in water-stress oil-producing countries, therefore, efficient treatment methods are required (Bilstad & Espedal, 1996). Hence, membrane filtration emerges as a promising technology in this field. Nevertheless, studies about the fouling mechanisms are very limited, most of them focused on the effect of the membrane material and hydrophilicity (Faibish & Cohen, 2001; Koltuniewicz et al., 1995). In this study, the efficiency of UF and MF membranes in removing oil from synthetic nanoemulsions was investigated. A close attention has been paid to size-related fouling mechanisms.