The surface oxidation of galena subject to various conditioning environments has been investigated by dissolution kinetics studies, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopies (XPS). A mechanism of oxidation involving the dissolution of lead and sulfide ions, their oxidation in solution or near the surface, the formation of lead sulfoxy species and lead carbonate, and their subsequent adsorption or precipitation on the galena surface has been proposed. The results of thermodynamic calculations based on this mechanism of oxidation have been found to be in agreement with the experimental results in predicting the lead and sulfur species in solution or on the surface at a particular pH and for a particular conditioning gas.