This research concerned choosing fluids and developing techniques for measuring coal porosity. Helium was adopted as the standard text fluid, and measurements made with it taken as the "true values." The boyle's law technique was adopted as the standard for measuring total (micro plus macro) porosity. Mercury-injection tests were found to provide significant information on pore-size distribution. Interest in coal porosity stems from its role in methane control in coal mines. An adequate definition of coal porosity and an acceptable method of measurement must provide links with this function. For this purpose, additional mercury-injection tests, studies of continuity of pore structures, coal microscopy, and stress tests were undertaken. Numerous specimens were examined. Porosity was found to be comprised largely of fractures, some undoubtedly caused by mining. Porosities ranged mostly between 2 and 5 percent. The findings provided a more realistic and substantial basis than existed before for involving porosity as a factor in methane control.