The case history of Leroy storage is unique because it involved definite migration away from the originally intended storage horizon as evidenced by seepage of gas to the surface. Several techniques were coordinated in an effort to understand, monitor, control, and reduce the leak. These included various logging, surveying, sampling, and testing techniques, tracer work, computer simulation, and engineering analysis. Among these, the computer simulation proved practical and effective in establishing a correlation between the leak rate and the extent of ''overpressure'' in the reservoir. The final evidence totally eliminating all appearance of leak to the surface is not yet on hand. There remains some work to be done before a collector zone is found and other measures to be taken such as recompletion, recycling, venting, pressure control, or whatever may be indicated. A computer program developed to simulate a unique