Rate measurements in the kinetically controlled regime, kinetic fittings, and isothermal C3H6 and O-2 uptake experiments lead to a proposed mechanism for C3H6 epoxidation and combustion reactions on predominantly O* covered Ag cluster surfaces. Epoxidation occurs via kinetically relevant reactions between chemisorbed oxygen adatoms (O*) and gas phase C3H6. In contrast, combustion occurs via kinetically relevant hydroperoxyl (OOH*) formation, formed from H transfer from H2O* to O-2* C3H6 oxidation reactions with C3H6-O-2-H2O-H2O2 mixtures show that H2O2 derived OOH* species are more effective oxidants than O* for C3H6 combustion, as confirmed from H2O2/D2O2 kinetic isotope effects. Both C3H6* and O* coverages are near or at chemical equilibrium during steady-state reactions, as confirmed from in-situ chemical titrations. C3H6P and COx site-time-yields and COx selectivities increase with increasing Ag cluster diameters and Ag surface coordination, because O*, O-2*, H2O*, and OOH* oxidants remain more weakly bound and therefore much more reactive. (C) 2018 Elsevier Inc. All rights reserved.