The invention is a process for epoxidizing an olefin with hydrogen and oxygen in the presence of a catalyst comprising a noble metal and a titanium or vanadium zeolite in a solvent mixture comprising water, methanol, and a C.sub.3 C.sub.6 aliphatic ketone. This process surprisingly gives significantly reduced by-product glycol and glycol ethers formed by the unwanted ring-opening of epoxides.