This paper presents a novel/cost-effective hydrophobic material based 9-octadecenoic acid grafted graphene (POG) for oil/water separation. Graphene derived from graphite was modified with 9-octadecenoic acid to obtain 9-octadecenoic acid grafted graphene (OG). Then, emulsion polymerization of styrene was performed on OG to produce polystyrene branches on 9-octadecenoic acid grafted graphene (POG). Three different composites were prepared by varying the amount of 9-octadecenoic acid grafted graphene used as follows: POG25, POG50, and POG75. The three materials were characterized by using N2-physisorption and Fourier transform Infra-red (FTIR). The BET surface area of POG75 was 288 m2/g while POG50 was 225 m2/g and POG25 was 79 m2/g. These materials were evaluated for their oil/water separation efficiency using model mixture. The results showed that the higher the ratio of the 9-octadecenoic acid grafted graphene, the higher the oil removal efficiency of the material and the faster the rate of the adsorption. The materials showed not only high efficiency but also fast uptake of the certain quantity of the oil just within 1 minute. This can be explained by the high hydrophobicity nature of the materials which repel the water as confirmed by the contact angle of approximately 150°. POG75 showed promising results to be a good candidate adsorbent materials for oil removal from produced water where it displays the highest adsorption capability to organic compounds and the highest BET surface area. POG75 was regenerated and its performance was tested again. This material showed a slightly reduced adsorption rate in the first cycle compared to the fresh material. However, the adsorption rate was constant for the next several cycles. POG75 has the potential to be utilized to remove oil contaminants from produced water.