The residual biaxial stress inAl2O3 scales formed duringoxidation of Fe-22.0%Cr-4.8%Al-0.3%Y in the temperaturerange 1000-1300°C have been measured usingCr3+ luminescence piezospectroscopy. Thestress measurements together with substantialdimensional changes of the specimens show that oxidationproduces high compressive growth stresses in theAl2O3 scale in addition tothermal-mismatch stresses that arise during cooling from the oxidationtemperature. The magnitude of the growth stress isdetermined by two opposing processes: stress generation,associated with lateral growth of the scale, and stress relaxation in both the metal and oxide. Thescale lateralgrowth strain continuously increasesconcurrently with the scale thickening. Creep in theoxide is a major relaxation process when the scale isthin, while metal deformation becomes significantduring the later stages of oxidation at highertemperatures.