The integrated membrane system is a promising technology for oily wastewater producing industries. The integrted membrane system achieves the high oil/water emulsions separation at the low-cost operation, however, its feed stream performance is hampered by membrane fouling which causes a decine in permeate flux and oil rejection ratio during the separation process. The poorly estimated transmembrane pressure in the integrated membrane feed stream leads to membrane pores blockages. When the transmembrane pressure builds up in the integrated membrane feed stream causes the decline in the oil/water rejection, which leads to poor membrane performance. The engineering equation solver software was used to model the transmembrane pressure for the optimal performance of the the integrated membrane feed stream during oil/water separation. The theoretical results obtained revealed that increasing the transmembrane pressure, will increase the permeate flux in the integrated membrane feed stream which optimizes the membrane performance. The unique methematical relationship was developed between the membrane pores and feed stream for optimal membrane performance during oil/water separation. Keywords— Integrated membrane, Feed stream, Oil-water separation, Transmembrane pressure, Pore size