The oxidation behaviour of two commercial FeCrAl alloys, Kanthal Al and Kanthal AF (containing alloying additions of yttrium), has been investigated during isothermal exposures in air at 1173 K. Mass gains were measured by thermogravimetry and identification of the oxidation products determined by in situ high temperature X-ray diffraction. The morphology of the oxide layer surfaces was studied by SEM, the elemental distribution inside the scales being carried out by EDXS analysis. The study revealed that yttrium markedly influences the composition and growth rate of the oxide scale during the steady-state stage of oxidation. The lower oxidation rate resulting from the presence of the reactive element reflects the influence of yttrium in suppressing the formation of transition alumina and promoting the earlier formation of a protective alpha-Al2O3 scale. (C) 2003 Elsevier Science B.V. All rights reserved.