Under appropriate conditions, single-crystal observations are capable of yielding information about reaction mechanisms and transport phenomena which can assist in understanding the behaviour of practical, high metal area, supported catalysts. In the case of chemical catalysis by metals, the literature contains a number of well documented examples of which illustrate the success of this approach. Corresponding model studies of the metal/oxide interface are less common, although in principle they should be capable of improving our understanding of those systems in which metal/support interactions play an important role in determining the catalytic chemistry. This paper deals with the application of such methods to two areas of synthesis gas chemistry; additionally, correlated measurements have been made on the structure and reactivity of the corresponding high-area catalysts. The usefulness of such a combined approach will be illustrated with reference to methanol synthesis over copper/rare-earth oxide systems and the behaviour of Ru/TiO catalysts.