Corrosion in sour downhole environments is one of the main challenges confronting operators in the Northern U.S. and Western Canada. Several research organizations around the world are working to develop models for characterizing hydrogen sulfide (H2S) corrosion and predicting sour corrosion rates. Unfortunately, the corrosion models developed so far are reliable for only low levels of H2S and can account for the influence of only a limited number of other variables.