The oxidation of type T22 steel was investigated at different temperatures in the presence of O-2 and O-2 + 100ppm SO2. The materials were oxidized at 400-800 degreesC for up to 72 hours using a thermobalance. The oxidized samples were investigated by a number of surface analytical techniques including grazing angle XRD, SEM/EDX, Ion Chromatography and XPS. The rate of oxidation of Fe-2.25Cr-1Mo steel in oxygen is suppressed by the presence of 100ppm SO2 at temperatures below 650 degreesC. SO2 has no effect on the oxidation rate at higher temperatures. The influence of SO2 is attributed to the traces of sulfate that form on the surface. At high temperature, sulfate formation is not possible because of thermodynamics. Exposure to SO2 also caused the formation of hematite whiskers. It is suggested that whisker growth is enhanced by the presence of sulfate on the surface. The oxide mainly consists of hematite. At temperatures above 700 degreesC small amounts of (Fe,Cr)(3)O-4 were found close to the oxide/metal interface.