Temperature-programmed desorption (TPD) and oxidation (TPO) were used to study decomposition and oxidation of methanol, ethanol, acetaldehyde, formic acid, and acetic acid on an Ag/Al2O3 catalyst. The volatile organic compounds (VOCs) were adsorbed on the alumina support. Silver was inactive for decomposition of adsorbed VOCs; all dehydration and dehydrogenation products evolved from reaction on the Al2O3 support during TPD. Silver was active for oxidation of VOCs during TPO, however, and a portion of the VOCs reacted on Al2O3 sites in parallel. Adsorbed VOCs reacted at silver sites with adsorbed oxygen; oxygen was supplied to silver sites from the gas phase, and surface diffusion on Al2O3 transported adsorbed VOCs to the silver sites. Adsorbed oxygen also activated neighboring silver sites for alcohol dehydrogenation in parallel with oxidation. Dehydrogenation was not observed for the aldehyde and acids.