Sol-gel derived Cu/ZrO2 catalysts have recently been shown to have high activity and selectivity toward methanol synthesis. TPR, TEM, in situ XRD and N2O decomposition have now been used to characterize the active sites in such catalysts over a wide range of Cu concentration. Copper is shown to be in two forms : surface aggregates (or particulate) and dispersed copper in the ZrO2 substitutional sites. The proportion of the former increases with an increasing Cu content, while the overall strength of the Cu-ZrO2 interaction simultaneously decreases. The activity in CO/CO2 hydrogenation showed no evident correlation with the total Cu surface area, but rather with the concentration of highly-dispersed form of copper. This is taken to indicate that the copper in the substitutional sites of ZrO2 is predominantly responsible for and associated with the active sites on Cu/ZrO2 for CO/CO2 hydrogenation.