There is a strong need to better understand the relation between the water content and the concentration of impurities in dense phase CO2 to be transported. At present there is a lack of data and therefore it is not possible to define the limits for the various impurities when they are mixed. Experiments have shown that corrosion takes place at a water concentration far below the water solubility in the pure water-CO2 system when impurities like SOx NOx and O2 are present. Particularly large effect and high corrosion rates are seen in the presence of NO2. The paper reviews published work and in-house data and discusses possible mechanisms and rate controlling parameters.