The treatment of oily wastewater continues to pose a challenge in industries worldwide. Membranes have been investigated recently for their use in oily wastewater treatment due to their efficiency and relatively facile operational process. Graphene oxide (GO) and silica (SiO2) nanoparticles have been found to improve membrane properties. In this study, a polyethersulfone (PES) based GO-SiO2 mixed matrix membrane (MMM) was fabricated, using the phase inversion technique, for the treatment of oil refinery wastewater. The PES/GO-SiO2 membrane exhibited the highest water flux (2,561 LMH) and a 38% increase in oil removal efficiency by comparison to a PES membrane. Compared to PES/GO and PES/SiO2 membranes, the PES/GO-SiO2 MMM also displayed the best overall properties in terms of tensile strength, water permeability, and hydrophilicity.