Sandia Laboratories fielded a comprehensive instrumentation effort on the Hanna II in situ coal gasification experiment conducted by the Laramie Energy Research Center in 1975-76. Instrumentation included temperature, electrical and seismic arrays designed to provide diagnostic information as well as to develop a remote monitoring capability to continuously map the in situ process. Three types of passive seismic signals produced by the gasification process were identified. The times of arrivals of discrete evvents were used to find the spatial origins of the seismic events by using a linear least squares technique. These seismic events were found to occur in the overburden above the burning coal seam and are related to subsidence. The seismic signals observed exhibited frequencies as high as 500 Hz and hence attenuated rapidly with distance. However, field data indicate that over 100 signals per day could be detected at 150 to 200 ft. from the source. Three dimensional plots of source locations are presented. These results correlate well with thermal data which provided direct and diagnostic measurements of the process.