The formaldehyde synthesis from methanol was investigated over a polycrystalline silver catalyst at temperatures up to 993 K. Water was added to the feed (water ballast process) like in the commercial BASF process. The conversion of methanol and the selectivity to formaldehyde appeared to increase with respect to the methanol ballast process with no added water. A long-time experiment was carried out lasting over more than 300 days time-on-stream. While the methanol conversion does not change significantly, there is a pronounced change in hydrogen and CO2 selectivity. A most noteworthy observation is that over months of operation, the width of the temperature region where formic acid is formed increases in a linear manner. Finally, interrupting the oxygen supply for a few hours led to a temporary deterioration of the product selectivity after oxygen re-admittance. All observations may well be interpreted in the framework of the commonly discussed silver-oxygen chemistry with its three different oxygen species (Oalpha, Obeta and Ogamma).