Abstract: A process is provided for epoxidation of an alkene in the presence of an oxygen-containing gas which comprises contacting the alkene and the oxygen-containing gas under epoxidation conditions in the presence of at least one gaseous efficiency-enhancing member of a redox-half reaction pair and a supported silver catalyst, the catalyst comprising a catalytically effective amount of silver on a solid porous support having a stability-enhancing morphology and an efficiency-enhancing amount of at least one efficiency-enhancing salt of a member of a redox-half reaction pair, the support having a surface area of at least about 0.7 m.sup.2 /g and a particulate matrix which contains particles having at least one substantially flat major surface.