A method of metering of hydrogen peroxide gas into an evacuated sterilization chamber is disclosed. The method includes the steps of continuously monitoring a pressure in the sterilization chamber； connecting a passage of known volume to the evacuated chamber for evacuating the passage； sealing the passage； connecting the evacuated passage to a supply of hydrogen peroxide solution for a time sufficient to draw the hydrogen peroxide solution into and fill the passage； sealing the passage； and repeating those steps until a preselected pressure increase in the sterilization chamber is detected. The pressure increase is preferably 19Torr. The known volume of the metering passage is preferably between 75 µL and 15 µL to control unwanted condensation of hydrogen peroxide in the sterilization chamber. Expensive peroxide concentration measurement systems are replaced with an economical low cost pressure sensor for control of the hydrogen peroxide concentration.
