Efforts were made at developing a simple catalytic epoxidation system for olefins using MoO3 and TBHP as terminal oxidant. Conversions of up to 92% and epoxide selectivities of up to >= 99% were obtained. The epoxidation reaction was accelerated by the addition of catalytic quantities of pyridine and pyrazole. The highest conversion was obtained with styrene (92%) and the highest selectivity with beta-methylstyrene (>= 99%). For the epoxidation of cyclohexene a number of decomposition products were obtained including a large proportion of 1-(tert-butylperoxy)-2-cyclohexene. Preliminary investigations appear to indicate the presence of peroxo Mo(VI) complexes in the epoxidation reaction mixture. (c) 2006 Elsevier B.V. All rights reserved.