A compact portable high-purity sensor for oxygen would be useful to gas suppliers for verifying purity in remote locations such as storehouses, delivery vehicles, and onsite at customer locations without having to bring the sample to the lab. High purity oxygen applications that could benefit include academic and governmental research, industrial cutting and welding, and municipal wastewater treatment. The sensor can serve as a complementary method to more complex laboratory analyses to check the purity of oxygen sources in the field. We will market commercial versions of the sensor to gas supply companies, research labs, and anywhere high purity oxygen is used. The sensor technique can also be adapted to other gases that have near infrared absorption lines, such as NH3, CH4, and CO2, which may find use in research and process quality control. NASA applications of the proposed sensor include on-orbit monitoring of oxygen from storage tanks to determine long-term structural stability as affected by chemical attack of tank and seal materials, monitoring of oxygen streams in wastewater aeration processes, and monitoring for leaks in oxygen storage systems. In addition, the sensor may find use in land based NASA activities such as monitoring of oxygen during purification processes and testing of oxygen purity at remote locations.