We performed steady-state activity measurements in microreactors to obtain the reaction rates for CO and H-2 oxidation. These reactions were studied on three different gold particle sizes (d approximate to 3.6, 5.7, 16.2 nm) using either O-2 or N2O as oxidizing agents. From our TEM analysis, our CO oxidation rates follow the d(-3) relationship proposed in Hvolbaek et al. [B. Hvolbaek, T.V.W. Janssens, B.S. Clausen, H. Falsig, C.H. Christensen, J.K. Norskov, Nano Today 2 (2007) 14-18]. Density functional theory (DFT) calculations on a Au{532} surface and a Au-12 cluster, which model corner sites, reproduced the apparent activation barriers of about 37 kJ mol(-1) for CO oxidation on the smallest nanoparticles by both O-2 and N2O. For all of the reactions studied, we found the overall activation barrier depended only on the size of the TiO2 supported gold nanoparticle. (C) 2008 Elsevier Inc. All rights reserved.