A study of corrosion for high pressure, large diameter pipelines under horizontal and 2 degrees oil/water/gas multiphase flow conditions was carried out. The water cuts studied were 10%, 20% and 30% ASTM saltwater. A light oil with viscosity of 2 cP was used as the oil phase. Carbon dioxide was used in the gas phase. The predominant flow was found to be slug flow and all corrosion experiments were carried out in this regime. Finally, the resulting data was analyzed.