An automated methane/total hydrocarbon analyzer was developed and flight tested that produced alternate methane/total hydrocarbon measurements every 7 s, providing the spatial resolution needed for regional hydrocarbon measurements at aircraft speeds. The sensitivity of the analyzer to oxygen and water vapor interference was characterized at appropriate concentrations. A technique to periodically measure atmospheric oxygen was determined to be necessary for accurate hydrocarbon measurements and incorporated into the analyzer. A data collection methodology was developed to minimize errors resulting from changes in flame ionization detector sensitivity at different altitudes (pressures). Selected aircraft data acquired during the 1979 Southeastern Virginia Urban Plume Study are presented to illustrate instrument performance.