The growth and oxidation of Mg films on polycrystalline cobalt foil have been studied using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, and work function measurements. At room temperature a simultaneous multilayers growth mode is observed. The formation of Mg multilayers can be prevented by holding the substrate at 550 K during Mg deposition. Both XPS and work function results suggest that adatom-adatom interactions are not important during overlayer growth. TDS data from oxidized Mg layers suggest a short-range interaction between Mg and O. An interesting relationship is observed between the Mg 1s binding energy and the oxidation state of the overlayer. At small oxygen exposures (below 0.4 L) the binding energy increases linearly. Above 0.4 L the binding energy decreases smoothly and levels off after 2 L.