Nanoindentation was utilized to induce fracture of brittle thin oxide films on compliant substrates. The energies were calculated from integrating the resulting load-depth curves from indentation. The total energy applied to the system is a superposition of the energy to deform the substrate and the energy to fracture the film. The applied energy to deform the compliant substrate was separated from the energy applied to the film/substrate system resulting in the energy to fracture the film. The energy for fracture was then converted to a crack extension force and a stress intensity using linear elastic fracture mechanics. The toughness of thermally grown aluminum oxides is between 0.37 and 0.83 MPa m(0.5) and tends to decrease as film thickness increases over the range of 25 to 63 nm. (c) 2006 Elsevier B.V. All rights reserved.