A non-dispersive infrared gas analyzer is disclosed that accurately measures the concentration levels of a plurality of gases within a gas mixture. The analyzer includes first and second sample cells and is utilized advantageously for the measurement of NO.sub.x and hydrocarbon gas present in the exhaust of an automobile engine. The gas mixture of the exhaust is chilled before entering the first sample cell to remove a substantial amount of the water vapor from that sample cell to facilitate measurement of the NO.sub.x gas. The second sample cell receives the gas mixtue in an unchilled state to allow for accurate measurement of the hydrocarbon gas. The analyzer includes processors which are utilized to further correct the NO.sub.x measurement and which also interact with each other to provide an output data stream that is representative of the concentration levels of the gases that are being analyzed.