In this Small Business Innovative Research (SBIR) effort, Los Gatos Research (LGR) proposes to develop a miniature, high-resolution, low power, triple-isotope water analyzer for lunar and planetary exploration based on tunable diode laser absorption spectroscopy (TDLAS) in conjunction with LGR's patented Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS) technique. This compact instrument will provide highly accurate quantification of H2^16O, HOD, H2^18O, and H2^17O (δD, δ18O, and δ17O to better than +or-0.3 and 00/100, +or-0.1 and 00/100, and +or- 0.15 and 00/100 respectively) with minimal calibration or consumable standards. In order to achieve this sensitivity and accuracy, Off-Axis ICOS employs a high-finesse cavity that increases the measurement path length to several kilometers, making it much more sensitive than conventional TDLAS methods which typically have path lengths ranging between several centimeters to several meters. Moreover, due to the inherent benefits of the Off-Axis ICOS technique, the analyzer will be selective, robust, and economical superseding other high-finesse cavity techniques (e.g., cavity ring-down spectroscopy). In addition to being a strong candidate for extraplanetary exploration, the resulting instrument will be deployed for field testing and research by scientists in NASA's Space Science and Astrobiology Division.