A principle of corrosion inhibitor behavior in an oil pipeline was studied with stearic acid and alkane. The role of corrosion inhibitor is explained by the function of surfactant, i.e., partition from oil to water, dispersion in water and adsorption on metal surface. Stearic acid alkane solution was treated as a single component model inhibitor. The performance of the model inhibitor was evaluated by measuring corrosion rates of carbon steel in a metal-oil-water system. Interfacial tension and total organic carbon were measured to investigate the dispersion of the model inhibitor. The corrosion rate was influenced by the carbon chain length of alkane, flow speed and pH of the test solution. The carbon chain length and flow rate seemed to affect the dispersion of the model inhibitor in the aqueous phase in association with the interfacial tension between alkane and water. Alkane dissociation at pH 5.5 seemed to accelerate the adsorption of the model inhibitor.