The size and number density of oxide nanoparticles in 9Cr-oxide dispersion strengthened (ODS) steels with different concentrations of excess O, Ti and W are quantitatively determined using small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). Based on the difference of the SANS and SAXS intensity in absolute units, the "alloy contrast variation (ACV) method" has been used to determine the compositions of the oxide nanoprecipitates. The results indicate that the finest size and highest number density of oxide nanoparticles is obtained by suppressing the amount of excess O and increasing the amount of Ti. The ACV method indicates that the finest oxide nanoparticles have a chemical composition close to Y(2)Ti(2)O(7). (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.