Results for the binding of carbon monoxide and oxygen along with the oxidation of CO in the presence of atomic Au- have been obtained utilizing a fast-flow reactor mass spectrometer. In addition, density functional calculations have been performed to explain the experimental findings. It was observed that upon oxygen addition to the metal plasma, gold oxide species of the form AuOn-, where n = 1-3, were produced. The addition of carbon monoxide to the preoxidized gold atom revealed that AuO- and AuO3- promote the oxidation of CO. Density functional calculations on structures and their energetics confirmed the experimental findings and allowed us to propose mechanisms for the oxidation of carbon monoxide. The reactions of CO with AuO1,3- proceed via complex formation with CO bound to the oxygen atom, followed by either cleavage of the Au-O bond or complex rearrangement to form a weakly bound CO2 unit, leading in both cases to the emanation Of CO2.