A hydroperoxide charge stock (t-butyl hydroperoxide or t-amyl hydroperoxide) is reacted with a C.sub.3 to C.sub.20 olefin charge stock in liquid phase in a reaction zone in the presence of a catalytically effective amount of a soluble molybdenum catalyst to form a product olefin epoxide corresponding to the olefin charge stock and a product alcohol corresponding to the hydroperoxide charge (t-butyl alcohol or t-amyl alcohol), which process is improved in accordance with the present invention by maintaining a reaction medium composed of more than 60 wt % of polar components (hydroperoxide charge stock, product alcohol and product epoxide) in the reaction zone by charging to the reaction zone at least about a 30 wt % solution of the hydroperoxide charge stock in the corresponding product alcohol and charging said olefin charge stock to said reaction zone in an amount relative to the amount of said charged solution of charged hydroperoxide in product alcohol sufficient to provide a ratio of from about 0.5 to about 2 moles of charged olefin per mole of charged hydroperoxide. The preferred olefin charge stock is propylene and the preferred hydroperoxide charge stock is t-butyl hydroperoxide. The corresponding epoxide in this situation is propylene oxide and the corresponding product alcohol is t-butyl alcohol.