An investigation was conducted to determine the feasibility of using reverse osmosis (RO) membranes to treat water containing up to 50% (by volume) oil. The effect of varying the feed pressure, pH and temperature oil separation performance of two thin film composite polyamide RO membranes was evaluated. In experiments involving contaminated water with up to 30% oil, high permeate quality was attained with more than 99% oil rejection being achieved. In some circumstances, oil contamination resulted in an increase in membrane flux and, as an example, at 50% oil contamination, an increase in membrane flux of 40% was observed. However, membrane permeate quality was deteriorating at these high concentrations. The product water quality improved significantly with decreasing feedwater pH and temperature effects on permeate quality were found to be minimal. It was observed that increased feedwater pressure leads to a significant improvement in permeate quality in terms of the total organic carbon (TOC). In this paper the observations from a comprehensive set of experiments are discussed in relation to the practicalities of using RO processes for oily water treatment.