AutoBlend is computer-controlled, multi-channel gas blending system for supplying continuous flow of adjustable composition test gas mixture. System can add multiple trace concentration components to flowing gas stream. Permeation tubes are used to add trace components to gas mixture. Concentrations from hundreds of parts-per-million down to low parts-per-trillion can be added. Component concentrations can be varied independently, making AutoBlend ideal tool for conducting statistically designed test programs.