The energetics of the water–gas shift (WGS) reaction (CO+H 2 O→CO 2 +H 2 ) over the oxygen-preadsorbed Cu(111), Cu(100), and Cu(110) surfaces has been studied by first-principle density functional calculations together with the UBI-QEP approach. Cluster models of the surface have been employed to simulate the adsorption of H, OH, and H 2 O on the atomic oxygen-preadsorbed Cu(hkl) surfaces at low coverage. Optimized results show that pre-adsorbed oxygen could intensify the adsorption of H, OH, and H 2 O on Cu(hkl) surfaces. Interestingly, oxygen-induced spontaneous dissociation of water has been found with pre-adsorbed oxygen in the 4-fold hollow site. Furthermore, it can be observed from energetic analysis that the WGS reaction can be promoted by pre-adsorbed oxygen either by its acting as a promoter or as a reaction intermediate. This promoting role of pre-adsorbed oxygen over Cu(hkl) surfaces for the WGS reaction is in accord with the experiments.