Liquid phase selective oxidations are normally catalysed homo­geneously. Significant interest has recently arisen in the use of solid cata­lysts for liquid-phase oxidations. Unlike similar studies[1-8] carried out on silver and gold, the present work is aimed at understanding the oxidation of copper and silver rather than the nature of adsorbed oxygen species. An inhibition technique was used to measure the radical initiation rate during liquid-phase cumene oxidation over copper and silver. The radical initiation rate was only slightly reduced by changing from an oxygen to an argon atmos