A novel and straightforward approach for the synthesis of mesoporous inorganic oxide nanoparticles, with a small particle size and high specific surface area is reported, by using oil-in-water microemulsions, in contrast to the typically used water-in-oil microemulsion method. The new strategy implies the use of organometallic precursors, dissolved in nanometer-scale oil droplets (stabilised by surfactant), and dispersed in a continuous aqueous phase. The potential of this approach is explored for producing nanocrystalline ceria, zirconia, ceria/zirconia mixed oxide and titania. Nanocrystalline cubic CeO2 and Ce0.5Zr0.5O2 were obtained under soft conditions, whilst ZrO2 and TiO2 presented wide X-ray diffraction peaks. The specific surface area (SSA) of the obtained materials was in the order of 200-370 m(2)/g and the particle size was very small (similar to 2-3 nm). The materials were calcined at 400 degrees C after which a high SSA was maintained (100-150 m(2)/g) and the crystallinity was improved, yielding tetragonal phases for both TiO2 (anatase) and ZrO2. The potential of the calcined materials as catalyst support was explored in the CO oxidation reaction by doping the oxides with Au (2 wt%). The obtained results demonstrate the feasibility of this approach for the preparation of various supports with high SSA for catalytic purposes. (C) 2010 Elsevier B.V. All rights reserved.