Recent underground coal gasification experiments at the Laramie Energy Researh Center field site at Hanna, Wyoming have been monitored with an array of subsurface thermocouples located in and near the coal seam. These temperature measurements are providing a quantitative basis for a specific understanding of thermal, chemical, and mechanical aspects of the underground gasification process. The subsurface measurements complement surface observations of process variables and allow direct deductions not avaliable from surface measurements alone. This paper presents a description of the thermometry system, an example of data validation using diagnostic information provided be branched thermocouple circuits, and complete temperature histories from four instrument wells during linkage, gasification, and cooldown stages of the Hanna II, Phase I experiment.