A 97Pb -- 3Sn alloy was oxidized at oxygen pressures below 10 mPa and temperatures from 20 degrees C to 200 degrees C. The reaction was monitored by Auger electron spectroscopy(AES). The oxide film formed most likely is SnO and is less than 2 nm thick. Lead is oxidized only if there is no tin at the surface. If tin can diffuse to the alloy surface sufficiently fast, lead will not be oxidized. Oxidized lead is reduced by metallic tin. -- AATA