Calculations estimate the temperatures and gross flow characteristics of the production-gas flare stack to be used in the Hoe Creek In-situ Coal Gasification Experiment No. 1. The temperatures are lowered somewhat by the expected presence of 10 to 30 mole percent water vapor in the production-gas stream. In the range of heating values typical of wet production gas (2.98 to 5.21 MJ/std m/sup 3/, or 80 to 140 Btu/scf), heat loss is small enough that the gas will sustain combustion if the water is vaporized, and the resulting temperatures are not beyond the stack's endurance. Some carbon-steel phase transitioning is expected to occur near the ends of the refractory hangers, but the problem should not be serious. An analysis of the pressure changes involved shows that the induced airflow is barely enough to ensure complete combustion of the production gases at the high production-gas flow rate of 1.42 std m/sup 3//s (3000 scfm). Since the calculations used to analyze the flare apply to any internal flare design, the calculational details are fully described.