A method for starting-up an alkylene oxide production process, the alkylene oxide production process comprising reacting a feed gas comprising an alkylene, oxygen, and at least one organic chloride over a high efficiency silver catalyst to yield a reaction product comprising the alkylene oxide, the start-up method comprising: providing a feed gas comprising the alkylene, oxygen, and the at least one organic chloride, wherein the feed gas has an overall chloriding effectiveness represented by the formula: Z * = ethyl chloride equivalent ppmv ethane equivalent mole % wherein the ethyl chloride equivalent is the total concentration in ppmv of ethyl chloride which provides substantially the same catalyst chloriding effectiveness of the at least one organic chloride in the feed gas at the concentration of the at least one organic chloride in the feed gas, the ethane equivalent is the total concentration in mole % of ethane which provides substantially the same dechloriding effectiveness as the non-chloride containing hydrocarbons in the feed gas at the concentration of the non-chloride containing hydrocarbons in the feed gas, and the feed gas has a Z* value ranging from 1.0 to 5.0; reacting the feed gas over the high-efficiency silver catalyst at a reaction temperature such that within a catalyst aging period of no greater than 0.03 kT alkylene oxide/m 3 catalyst after the reactor is first on-stream, the reaction temperature is from 215°C to 240°C, and the molar ratio of oxygen to the alkylene in the feed gas is at least 0.2, thereby yielding a reaction product comprising a start up concentration of the alkylene oxide; wherein the said high efficiency silver catalyst is a catalyst capable of producing an alkylene oxide from the corresponding alkylene and oxygen at an efficiency greater than 85.7 percent. providing a feed gas comprising the alkylene, oxygen, and the at least one organic chloride, wherein the feed gas has an overall chloriding effectiveness represented by the formula: Z * = ethyl chloride equivalent ppmv ethane equivalent mole % wherein the ethyl chloride equivalent is the total concentration in ppmv of ethyl chloride which provides substantially the same catalyst chloriding effectiveness of the at least one organic chloride in the feed gas at the concentration of the at least one organic chloride in the feed gas, the ethane equivalent is the total concentration in mole % of ethane which provides substantially the same dechloriding effectiveness as the non-chloride containing hydrocarbons in the feed gas at the concentration of the non-chloride containing hydrocarbons in the feed gas, and the feed gas has a Z* value ranging from 1.0 to 5.0; reacting the feed gas over the high-efficiency silver catalyst at a reaction temperature such that within a catalyst aging period of no greater than 0.03 kT alkylene oxide/m 3 catalyst after the reactor is first on-stream, the reaction temperature is from 215°C to 240°C, and the molar ratio of oxygen to the alkylene in the feed gas is at least 0.2, thereby yielding a reaction product comprising a start up concentration of the alkylene oxide; wherein the said high efficiency silver catalyst is a catalyst capable of producing an alkylene oxide from the corresponding alkylene and oxygen at an efficiency greater than 85.7 percent.