"Values of absolute permeability to gas and porosity for Pittsburgh, Hanna, and Gillette coals are presented. Effective and relative permeability's to gas as functions of water saturation and flow orientation are also calculated from steady-state Darcian flow experiments. The rate of increase in permeability to gas past the critical gas saturation is significantly greater as the rank of the coal decreases. Similarly values of absolute permeability, shrinkage, and porosity are inverse functions of rank. Values of the former range over three orders of magnitude. The critical gas saturation does not appear to be a function of rank."