The gold-catalyzed aerobic oxidations of alkenes are thought to rely on the in situ synthesis of hydroperoxide species, which have however never been clearly identified. Here, we show direct experimental evidence for the presence of 1-methylcyclohexyl hydroperoxide in the aerobic co-oxidation of stilbene and methylcyclohexane catalyzed by the Au/SiO2-R972 optimized catalyst prepared in Part I. Determination of its response in gas chromatography, by triphenylphosphine titration followed by P-31 NMR, allows to easily follow its concentration throughout the co-oxidation process and to clearly highlight the simultaneous existence of the methylcyclohexane autoxidation pathway and the stilbene epoxidation pathway. (C) 2012 Elsevier B. V. All rights reserved.