Techniques for detection and measurement of carbon monoxide (CO) in air are of interest and utility in many aspects of automotive safety. CO concentrations may range from less than 100 parts per million (ppm), or 0.01 percent, to about 10 percent by volume. Gas indicator tubes have been used for many years primarily as detectors of hazardous gases in a work environment. These tubes contain a chemical filling; the concentration of a specific gas is indicated by a change in color of the filling. If such tubes could provide satisfacotry precision for a given application, they appeared to offer a potentially low cost solution to this measurement problem. The objective of the study was to determine the accuracy and reproducibility achievable in the measurement of carbon monoxide concentrations using length-of-stain gas indicator tubes. (NTIS)