Abstract: Ethylene oxide is prepared by supplying a gaseous mixture containing ethylene, oxygen and a moderator of the oxidation reaction to a first reaction zone containing a silver-based catalyst, cooling the gas stream leaving this zone, supplying it after enrichment with oxygen and moderator to a second reaction zone containing the silver-based catalyst, recovering ethylene oxide and recycling the residual gases after being combined with fresh reacting gases, the reaction temperature of the second zone being at least 5.degree. C less than the temperature of the first zone.