Two chromia forming materials have been exposed to different test gases at low pO2. All used test gases contained hydrogen species in the form of molecular hydrogen and water vapour. To insure the validity of the measured H-profiles H2 was replaced by with D2 and H2O by D2O. The Deuterium profiles in the oxides formed were established using SIMS and GDOES techniques. The profiles were quantified and correlated with the growth rate and the microstructures of the chromia scales formed on in low pO2 test gases. The presence of H2/H2O in the low pO2 test gas alters the properties of thermally growing chromia scales.