Abstract: This invention relates to a process for starting up a fixed bed ethylene oxide reactor containing a catalyst comprising silver, alkali metal promoter and rhenium co-promoters supported on an alumina carrier which process comprises heating the reactor to slightly below normal operating conditions, passing an ethylene containing gas over the catalyst at a flow rate of about 20% of design, adding a chlorohydrocarbon moderator to the gas passing over the catalyst and after approximately 1 cubic centimeters of moderator (basis liquid) per cubic foot of catalyst has been added, then adding oxygen to the gas passing over the catalyst to initiate the ethylene oxidation reaction and subsequently raising the reactor temperature and gas flow rates to operating conditions.