In this STTR Phase I effort, Los Gatos Research (LGR) and Professor Scott Sanders (Mechanical Engineering Department, University of Wisconsin -- Madison) propose to develop a highly-accurate sensor for high-purity oxygen determination. The analyzer, which is based on near-infrared tunable diode laser absorption spectrometry (TDLAS) and LGR's patented Off-Axis Integrated Cavity Output Spectrometry (Off-Axis ICOS), will be capable of rapidly quantifying high-purity oxygen (95 -- 100 %) with very high accuracy (to better than ± 0.05 %), minimal calibration, and no zero drift. The analysis will be completely specific and exhibit no measurable cross-interferences from other background species (e.g. argon, nitrogen, water vapor, CO, CO2, or small organics). Moreover, the analyzer will be low-power, battery-operable, require no consumables, and sufficiently compact and robust for adaptability to future space missions. The high-purity oxygen sensor will help characterize NASA oxygen generators for breathing and propulsion applications.