The compounds La2-xSrxNiO4+delta, x = 0, 0.1, have been prepared with an oxygen excess of up to delta = 0.24. The oxygen tracer diffusion coefficient Md surface exchange coefficient of the materials have been determined by the isotope exchange depth profile method (IEDP). La2NiO4+delta was found to have an oxygen diffusivity higher than that of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and one order of magnitude lower than the best perovskite oxide ion conductor La0.3Sr0.7CoO3 (LSC). The fast oxide ion diffusion of La2NiO4+delta combined with its thermal stability indicate that this material would be a good candidate for use in ceramic oxygen generators (COGs) and solid oxide fuel cells (SOFCs). Furthermore, optimisation by a combination of donor and/or acceptor doping should improve the properties reported here. (C) 2000 Elsevier Science B.V. All rights reserved.