The passivity and electrochemical behavior of single crystalline, ordered NiAl intermetallic compound in buffered solutions of pH 2, 7, and 12.5 was compared to that of polycrystalline Ni and Al. NiAl exhibited improved passivity compared to Ni at a pH of 2, and improved passivity compared to Al at pH 12.5. Water oxidation and reduction were enhanced on NiAl compared to Al, suggesting the presence of a more conductive or catalytic oxide film. Al2O3 was preferentially formed (> 60 atom % of all oxidized Ni and Al species) throughout the interior of oxide films formed anodically at each pH as well as within the air-formed oxide grown at room temperature. However, the oxide surface layers exhibited a tendency toward nearly equal presence of oxidized Ni+2, especially as the pH was increased to 7 and 12.5. Therefore, Al2O3 formation was favored, but not exclusively, during electrochemical passivation. In contrast, little or no Ni+2 las NiO or NiAl2O4) has been reported after high temperature oxidation of NiAl. The composition of the electrochemically grown oxide is influenced by the specific oxide solubility and kinetic formation/dissolution rates at the oxide/solution interface as well. as by the free energy of formation of the oxides.