Systems and methods for producing a product gas are provided. In one embodiment, a system includes at least one separation bed to separate adsorbable components from a gas source, a valving means to selectively direct gas from the gas source to the at least one separation bed, at least one sensing device associated with the at least one separation bed to sense the progress of an adsorption zone within the separation bed, and a controller. The controller includes logic to read the output of the at least one sensing device and control the gas separation process based on the progress of the adsorption zone.