Southwest Sciences proposes to continue the development of a rugged, compact, and automated instrument for the high sensitivity measurement of tropospheric carbon monoxide (CO) and methane. The application of recently developed room temperature vertical cavity diode lasers (VCSELs)operating near 2300 nm permits the development of sensitive and rugged instrumentation for measurement of both atmospheric CO and methane with high precision. Phase 1 efforts successfully addressed the feasibility of measuring CO to a precision of 10 parts-per-billion or better over a range of tropospheric temperatures, pressures, and humidity. Phase 2 will extend the technology to simultaneous measurement of both carbon monoxide and methane. The principal objective is the development of prototype instrumentation for field testing.