A set of experiments was conducted to determine the origin of residual stresses in amorphous Al2O3films formed by ion beam assisted deposition. Samples were deposited during bombardment by Ne, Ar, or Kr over a narrow range of energies,E, and a wide range of ion‐to‐atom arrival rate ratios,R. Films were characterized in terms of composition, thickness, density, crystallinity, microstructure, and residual stress. Film composition was independent of ion beam parameters and residual stress was independent of thickness over the range 200–1200 nm. Stress varied strongly with ion beam parameters and gas content. Residual stress and gas content saturated at a normalized energy of ∼20 eV/atom or anRof ∼0.05. Where residual stress varied linearly withRE1/2, results are consistent with an atom peening model, but saturation at highRorRE1/2is inconsistent with such a model. Stress due to gas pressure in existing voids explains neither the functional dependence on gas content nor the magnitude of the observed stress. A probable explanation for the behavior of stress is gas incorporation into the matrix, where the amount of incorporated gas is controlled by trapping. ©1995 American Institute of Physics.