Optical ellipsometry, Auger electron spectroscopy and low energy electron diffraction were applied to determine the initial sticking coefficient S0 and the interaction kinetics of oxygen and atomically ordered and disordered (110), (111) and (111) surfaces of GaAs. The activation energy of S0 for disordered surfaces was obtained. This information is used to suggest a surface disorder mechanism for oxygen interaction with these surfaces. © 1979.