New results from the catalyst-free epoxidation route for small alkenes in the homogeneous gas phase using 03 as the oxidizing agent (Berndt, T.; Boge, O.; Heintzenberg, J.; Claus, P. Ind. Eng. Chem. Res. 2003, 42, 2870.) are presented. The formation of propylene oxide was studied in a wide range of experimental conditions such as total pressure, temperature, feed composition, residence time, and reactor dimension. In the absence of dilution gas, for a propylene conversion of 91.8%, a selectivity to propylene oxide of 93.3% was found. An optimal 03 utilization of similar to95% (reacted propylene/initial O-3=0.95) was achieved by limiting the propylene conversion to 20-30%. The epoxidation of ethylene yielded a selectivity to ethylene oxide of 90% and better in a wide range of conditions. The maximum formation rates of propylene oxide and ethylene oxide measured were 3640 and 2870 g per hour and per liter of reaction volume, respectively.