Blending two or three gases in homogeneous infinitely variable concentrations directly at the end use point, this model G gas proportioner is unsurpassed in convenience and economy. The Gas proportioners pay for themselves since they eliminate the need for expensive custom blended gas mixtures. They lend flexibility and economy to the utilization of component gas cylinders and “piped-in” supply lines. Another advantage in laboratory investigations is the freedom to reproducibly increase or decrease concentrations during the course of an experiment.