The use of corrosion inhibitors in multiphase flow environments consisting of oil/water mixtures is common in a variety of industries. Frequently oil is assumed to reduce uninhibited corrosion rate which could lead to lower required concentrations of inhibitor to maintain protection. In this paper we present the results of a study of inhibited corrosion in multiphase flow. These results are obtained from a novel three-cell flow loop (EC3) that is capable of simultaneous independent measurement of corrosion erosion and erosion-corrosion. The efficiency of inhibitor in oil-water flow is measured at three water-cuts 100% 40% and 20%. Increasing oil content was found to lower the baseline 0 ppm inhibitor corrosion rate when decreasing water cut from 100% to 40%. Further decreasing water-cut did not have a statistically significant effect. Increasing oil content was found to reduce inhibitor surface coverage likely due to a combination of adsorption of inhibitor to oil-water interfaces and dissolution of inhibitor in the oil phase.