The interaction of water vapor with the Ni-3(Al, Ti)(100) and polycrystalline Ni3Fe surfaces, with and without the presence of oxygen, was studied with Auger electron spectroscopy, photoemission, thermal desorption, and isotope scavenging. Water dissociates to produce atomic hydrogen above 200 K on the Ni3Fe surface. Preadsorbed or coadsorbed oxygen on both Ni-3(Al, Ti) and Ni3Fe surfaces suppresses hydrogen production due to water dissociation. This suppression process occurs more efficiently on Ni3Fe than Ni-3(Al, Ti).