The effect of gas velocity on the oxidation of three chromia-forming steels; X20 (11%Cr). 304L (18%Cr) and 310 (25%Cr) in O-2+40% H2O at 600 degreesC is reported. The samples are investigated by a number of surface analytical techniques including grazing angle XRD, SEM/EDX, and SAM. At low gas velocities a protective chromium-rich oxide forms on X20 and 310 while 304L shows partly protective behavior. With increasing gas velocity, the oxide tends to becomes more iron-rich and, consequently, less protective. The influence of gas velocity in O-2/H2O environment is explained by the loss of chromium from the oxide through evaporation. The volatile species is suggested to be CrO2(OH)(2). The different behavior shown by the three materials is explained in terms of the supply of chromium from the substrate to the ox-ide. Chromium depiction results in an increase in corrosion rate with gas velocity for all three materials and to "breakaway corrosion" in the case of X20.