Nickel and iron-base alloys containing 1.5 wt.% aluminium and various low level chromium additions were internally oxidised at 1000degreesC. Penetration kinetics were invariably parabolic and rates were found to be controlled by inward oxygen diffusion. This was accelerated in the presence of acicular, aluminium-rich oxide precipitates, aligned approximately normal to the alloy surface. Chromium alloy additions led to precipitate coarsening and, at lower oxygen activities, to loss of acicular character. This effect could not be accounted for using classical nucleation theory, but was qualitatively consistent with a kinetically controlled mechanism.