Two types of experiments were carried out to study the oxidation behaviour of NiCr-base model alloys; thermogravimetric measurements for up to 72h exposure at 1000°C in synthetic air and isothermal exposures for up to 100h at 1000°C in laboratory air and in Ar–4%H 2 –2%H 2 O. It was found that there is a significant effect of specimen thickness on the oxidation rate of all studied alloys. The growth rates of the chromia scales decrease with increasing specimen thickness in both air and the Ar–H 2 –H 2 O mixture. Based on the present results in combination with recent literature data for ferritic steels, it is postulated that the decrease in rate is the result of compressive growth stresses in the scales which can relax by plastic deformation of the substrate for thin specimens but are maintained at significant levels for thick specimens.