The computer based instrumentation system described herein provides a very effective means of monitoring and controlling an in situ coal gasification installation. The benefits of such a system have been proven by several in situ coal gasification field experiments. Past and present process data such as flow rates, pressures, temperatures, and gas composition are immediately available. Computer automatic control maintains air injection rates with great precision and can be used to automatically change air injection rates in response to changes in other process parameters. In addition, many routine duties are no longer required to be performed by the operators.