We have used molecular dynamics simulations and energy minimization calculations to examine defect energetics and oxygen diffusion in ytttia-stabilized zirconia (YSZ). Oxygen vacancies prefer to be second nearest neighbors to yttrium dopants. The oxygen diffusion coefficient shows a peak at 8 mol% yttria consistent with experimental findings. The activation energy for oxygen diffusion varies from 0.6 to 1.0 eV depending on the yttria content. The Y-Zr'-V-O-Y-Zr' complex with a binding energy of -0.85 eV may play an important role in any conductivity degradation of YSZ. (c) 2006 Elsevier B.V All rights reserved.