Mathematical models are developed tor the prediction of corrosion rates in large diameter, high pressure, horizontal multiphase oil/water/gas pipelines. The models quantify the effects of multiphase flow characteristics, such as phase distribution, turbulent intensity, wall shear stress, and pressure drop, on the corrosion processes at the metal surface. Mechanisms are presented for both full pipe flow and slug flow. The models incorporate the effects of fluid properties, pressure, temperature, and pipe diameter, on corrosion rate. In full pipe oil/water flows, the corrosion rate can be predicted as a function of the total wall shear stress for a given carbon dioxide partial pressure and temperature. In slug flow, the effect of the liquid composition becomes significant, and the total shear stress is difficult to calculate. In this case, the pressure gradient across the slug can be correlated with the corrosion rate for a given liquid composition, at a particular carbon dioxide partial pressure and system temperature.