Segregation phenomena of group 10 (M = Ni, Pd, Pt) transition-metals substituted in Au (1 1 1) surface and sub-surface layers are investigated by DFT periodic calculations in presence of adsorbed atomic and molecular oxygen. In contrast with vacuum conditions, where the metal impurities M prefer to be in the bulk of gold, in the presence of adsorbed O or O2, the impurities mainly segregate to the surface. The analysis of oxygen adsorption trends and electronic surface structures explain the change in the local atomic arrangement which is expected to occur on the surface of alloys during reaction conditions.