Abstract A limited number of papers report experimental corrosion data in the presence of flue gas impurities like SO x , NO x and O 2 . When SO 2 , water and O 2 are present, sulphurous and/or sulphuric acid (H 2 SO 3 and H 2 SO 4 ) might form. The minimum water concentration required for acid formation is not known, but the presence of FeSO 3 and/or FeSO 4 on the corroded surface in some experiments indicate that the reactions occur at water concentrations far below the water solubility in pure CO 2 -water systems. The corrosiveness increases considerably when NO x is present. NO 2 is highly soluble in water and reacts with water to produce nitric acid and NO under atmospheric conditions. The same type of reaction probably occurs in the dense phase CO 2 system. Experimental results indicate that the rust-like dusty products formed does not efficiently reduce the corrosion rate. There is limited number of papers presenting data and discussing the effect of combined impurities on corrosion. When both, NO 2 and SO 2 are present, NO 2 catalyzes the oxidation of SO 2 to form sulphuric acid. In addition, in the presence of H 2 S, elemental sulphur can form. Such interactions between impurities are especially dangerous when network pipeline systems are considered and CO 2 streams from different sources and with different impurities are mixed. As a result two non-corrosive streams can become very corrosive if highly corrosive acids are formed as a result of the reaction between added impurities.