The oxidation of methyl formate on oxygenprecovered Au(332) was studied by temperature-programmed reaction (TPR) spectroscopy and infrared reflection absorption spectroscopy (IRAS) under well-defined ultrahigh vacuum conditions. Methyl formate was found to bind more strongly and with a significantly altered adsorption geometry upon oxygen precoverage of Au(332) (O/Au(332)) compared to pristine Au(332). TPR experiments evidence oxidation of methyl formate for low oxygen coverage (0.13 ML) at low temperatures. In particular, three discernible channels resulting in CO 2 desorption at 135, 185, and 320 K could be identified. Isotopic labeling experiments with preadsorbed 18 O reveal different ratios of CO 2 isotopologues for the different reaction channels, suggesting different underlying reaction mechanisms, namely, the attack of oxygen to the carbonyl carbon or the methyl carbon of methyl formate. The desorption at 320 K is found to result from the decomposition of formate, which is formed at around 200 K and adsorbs at specific surface sites. The oxidation of methyl formate at low temperatures and low oxygen coverages renders these reaction channels possible pathways to deteriorate the selectivity of catalytic methanol oxidation to methyl formate on gold surfaces.