In this Small Business Innovative Research (SBIR) effort, Los Gatos Research (LGR) proposes to employ its patented mid-infrared Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS) technique to develop a compact OCS, CO2, and CO analyzer. This sensor will provide rapid (up to 10 Hz), real-time, highly accurate (OCS, CO2, and CO to better than plus or minus 20 pptv, plus or minus 0.2 ppmv, and plus or minus 5 ppbv respectively, 1 sigma at 1 Hz) measurements of these important trace gases with minimal calibration. The instrument will also report water vapor concentrations for calculations of dry mole fractions. Moreover, the SBIR instrument will be capable of both terrestrial and airborne deployments (e.g. DC-8, WB-57, ER-2, Alpha Jet...) to provide data in the troposphere, tropopause, and stratosphere. The resulting system will allow researchers in NASA's Earth Science Division to acquire data that complements satellite observations made from several missions in the Earth Observing System (EOS). The in-situ data will provide higher spatial resolution and vertical profiling near highly inhomogeneous OCS and CO2 sources, helping to better understand stratospheric aerosol loading and gross CO2 flux between plants and the atmosphere, both critical needs for improved climate modeling.