Catalyst performance of both promoted and unpromoted Ag/Al2O3 catalysts for the epoxidation of butadiene is summarized and compared to temperature programmed reaction data for the reaction of butadiene with submonolayer coverages of oxygen on Cu(Ill) that has been presented in the literature (6). The role of the alkali promoter salts used for the supported silver catalysts is compared to the role of Cs metal deposited on the Cu(111) surface with respect to changing catalyst performance. The comparison indicates that, unlike the previously published data, silver catalysts, and in particular, promoted silver catalysts, are far superior to their copper counterparts. For the Cu(111) case, reaction of adsorbed butadiene with adsorbed oxygen is especially selective for the formation of 3,4-epoxy-1-butene. However, this reaction is best described as a Cu-mediated, substoichiometric reaction between adsorbed butadiene and adsorbed oxygen. Unlike Ag catalysts, activity of the Cu(111) surface is highly dependent upon maintaining the surface as Cu degrees, not the thermodynamically more favored Cu2O state.