Abstract: In a method of preserving in a storage vessel a volumetric ratio of a calibrating gas mixture within a range from below 1 vpm to about 10,000 vpm, wherein the calibrating gas mixture includes a carrier gas and a predetermined trace of another gas, and the storage vessel has inner steel walls electroplated with a metal selected from the group of tin, zinc, nickel and lead, the selection depending on the mixture, the steps include introducing the gases into the storage vessel under relatively high pressure of not more than 200 atmospheres, storing the gases in the storage vessel, so as to preserve the volumetric ratio between the gases within a predetermined accuracy, transporting the gas mixture within the storage vessel, and discharging the calibrating gas mixture from the storage vessel while still retaining the volumetric ratio.