Ultrahigh vacuum-deposited (111) oriented thin Alms of Al were oxidized at temperatures from 300 to 600 K with O2 pressures from 25 to 600 Torr, using in situ ellipsometric measurements to monitor oxide growth and optical properties. Al2O3 films with thicknesses from ~13 to 35Å were formed with exposure times varying from a few to almost 10,000 min. These oxide layers were slightly light absorbing, indicative of the presence of dopant levels of excess Al. The experimental data were analyzed on the basis of an inverse logarithmic growth law. © 1982, The Electrochemical Society, Inc. All rights reserved.