"The Laramie Energy Technology Center has conducted several in situ field experiments for the recovery of fossil fuel substances. This paper describes the data acquisition and process control instrumentation that was used during recent in situ field experiments in tar sand combustion, oil shale retorting, and underground coal gasification. Specifics to be discussed include instrumentation for automatic gas sampling and analysis, underground temperature and pressure instrumentation, pressure and flow measurement and control, hardware configurations, and the software systems used to monitor, control, and record the processes. The paper also includes comparisons of the instrumentation, computer hardware, and the software used on each of the three most recent experiments. The best features of these systems can now be adapted to future applications in the field or in the laboratory."