Gold nano-particles supported on metal oxides are active in a number of heterogeneous catalytic processes such as low temperature CO oxidation, propylene epoxidation, hydrogenation reactions, the reduction and decomposition of NO and NO2. It has been observed that gold nano-particles adsorbed on reducible oxide supports (TiO2, Fe2O3, Ce2O3) are more reactive in a number of oxidation reactions than the Au particles dispersed on irreducible oxide supports (Al2O3, SiO2) at identical external conditions and for gold nano-particles of equal size. We have employed Density Functional Theory (DFT) calculations to investigate oxygen adsorption and dissociation over a number of Au/oxide systems. These studies have revealed mechanistic insights regarding the effect of oxide supports on Au/oxide chemistry. We find that oxide supports not only provide anchoring points for gold nano-particles but also can significantly and predictably alter the chemical behavior of the nano-particles.