Estimates of the energy balance for the first underground coal-gasification experiment at Hanna, Wyoming, have been calculated for a 5 1/2-month period from mid-September 1973 through February 1974. Operating results were the most favorable during this period, with dry gas production rates averaging 1·6 million scf/day (45,300 Nm /day) at an average gas heating value of 126 Btu/scf (1122 kcal/Nm3). The ratio of energy produced to energy consumed in running the experiment was approximately 4, and the overall efficiency was approximately 50%. Use of more efficient air compression equipment and of a system designed for combustion of low-Btu gas could increase this ratio to 8 and efficiency to 55%.