A rugged yet simple burner that can be easily ignited and reignited is a necessity if in situ thermal methods of energy extraction are to be feasible. During extraction trials at the Dow Chemical Company's oil shale site at Peck, Michigan such a burner was utilized. The performance of the TOR Development burner and ignitor system proved to be reliable and practical under field conditions. However, some recently discovered measures are crucial in protecting the burner and associated downhole hardware. With such precautions burner life was extended by a factor of 15. In the first trial burner life was two days and in the second trial the burner remained intact at least thirty days. Also described is a system which monitored burner performance by continuously analyzing burner exhaust gases. A slip stream sampling technique utilized the high well pressure to transport, at nearly Mach I, a sample of burner exhaust gas to the analytical trailer. There the sample was analyzed for CO, CO/sub 2/, unburned hydrocarbons, and O/sub 2/ by a bank of high speed process gas analyzers. Burner flameouts could be detected in less than 2 minutes. Also the system allowed burner (air/fuel) ratios to be determined on a real time basis. These ratios were used for (1) setting the proper air-fuel mixtures for ignition and steady state operation, (2) leak detection, (3) estimation of burner deterioration after extended use, and (4) study of the burner's steady state and transient response characteristics.