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The fourth underground coal gasification experiment conducted by the Laramie Energy Technology Center is currently underway at a site near Hanna, Wyoming. The Hanna IV experiment, as originally conceived, was significantly larger than the three previous experiments. The experiment was designed to meet the following objectives: determination of the interrelationships of well spacing, air injection rate, and areal sweep efficiency; demonstration of the ability to conduct reverse combustion linkage over distances up to 45.7 m (150 feet); determination of pressure and gas composition gradients within the coal seam during process operation; determination of gasification zone progress as a function of time; and demonstration of relaying the process down a row of process wells.A portion of the technology development has involved environmental assessment of the process. This assessment included characterization of the effluents from the process as well as initiation of biological effects studies and determination of the fate of pollutants from the process. Major concerns associated with the process are impacts on air and ground water quality and the effects of subsidence. This paper describes the initial phase of the Hanna IV experiment in which difficulties were encountered and a sustained gasification process could not be maintained. An override situation across the 30.5 m (100-foot) well spacing resulted in a premature shutdown of the experiment. Preparations are being made to continue the experiment and recover from the override situation.