This paper describes some experiments on the oxidation of evaporated aluminium films in the temperature range 323–673 K. The kinetics were followed by measuring the rate of increase in resistance as the film was consumed by oxidation. The effect of suddenly altering the oxygen pressure on the oxidation rate was studied as a function of time and oxidation temperature. In the pressure range studied (ca. 1 × 103–30 × 103 N m–2 of oxygen), pressure increases were always associated with rate increases and pressure decreases with rate decreases. The effect of the pressure change on the reaction speed was found to diminish somewhat as the oxidation progressed, and also decreased with temperature. These results have been interpreted in terms of a modified Mott-Cabrera theory.