In this Small Business Innovative Research (SBIR) effort, Los Gatos Research (LGR) proposes to employ mid-infrared Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS) to develop a compact, rugged analyzer to quantify low concentrations of 12CH4 (methane), 13CH4 (delta_13C of methane), C2H6 (ethane), C3H8 (propane), and C4H10 (butane) in the gas phase. This portable instrument will provide rapid (0.1 1 Hz), highly-accurate quantification of these gasses with minimal external calibration or consumables. The target accuracies for the measured species are [CH4] to better than plus or minus 0.05 0.1 ppbv, delta_13C of ambient CH4 to better than plus or minus 0.5 1 and 00 over 100, [C2H6] to better than plus or minus 0.05 1 ppbv, [C3H8] to better than plus or minus 0.1 1 ppbv, and [C4H10] to better than plus or minus 0.1 5 ppbv. The resulting instrument will allow researchers in NASA's Space Science and Astrobiology Division to perform field measurements of methane and other hydrocarbons in order to better discriminate between biotic and abiotic methane production. These studies are widely applicable to the exploration of Mars, and the technology can be miniaturized to address this critical NASA need. These in-situ terrestrial measurements also provide valuable high-resolution data for the calibration of remote sensing instruments.