The reactivity of H-2 gas with the In and Sn surfaces was quantitatively measured by a volumetric method at pressures ranging from 10(-7) to 10(-2) Pa at 298 K. Significant enhancement of H-2 reactivity was observed when O-2 or H2O preadsorbed on the surface of In and Sn before H-2 exposure. The formation of the oxygen deficient SnO2 -x and In2O3-z in the surface layers is proposed as a reason for such a facilitating the H-2 dissociation and resulting in the enhancement of the H-2 reactivity at 298 K. (C) 2009 Elsevier B.V. All rights reserved.