Previous studies have shown that alloying occurs when indium deposits equivalent to a few monolayers are evaporated onto Au (111). This article compares the initial oxidation of the ultrathin alloy to that of polycrystalline bulk indium. Auger electron spectroscopy, electron energy loss spectroscopy, low energy electron diffraction, and work-function change measurements were conducted under ultrahigh vacuum conditions at room temperature. Oxidation of the polycrystalline sample follows first-order Langmuir kinetics, and saturates by 1 X 10(3) L (1 L = 10(-6) Torr s), to form a 4.5 Angstrom thick oxide layer. The stoichiometry of the compound is In2O3. The oxygen uptake of the alloy saturates with less than two layers of In-Au alloy present, and an oxide layer of different stoichiometry is generated, 4.2 Angstrom thick. It is suggested that gold may be participating in the alloy stoichiometry. The results are compared to another study of oxidation of bulk indium.