The local environments for oxygen in yttrium-containing pyrochlores and fluorites, Y-2(B1-xB'(x))(2)O-7 (B = Ti, B-' = Sn, Zr) are investigated by using solid state O-17 MAS NMR spectroscopy. The quadrupolar coupling constants of the I = (2)/(5) nucleus, O-17 are sufficiently small for these ionic oxides, that high-resolution spectra are obtained from the MAS spectra. Different oxygen NMR resonances are observed due to local environments with differing numbers of metal cations (Y3+, Sn4+, Ti4+ and Zr4+), allowing the numbers of different local environments to be quantified and cation mixing to be investigated. Evidence for pyrochlore-like local ordering is detected for Y2Zr2O7, which nominally adopts the fluorite structure. (C) 2003 Elsevier Inc. All rights reserved.