The effective and relative permeabilities of Gillette, Wyoming sub-bituminous and Pricetown, W. Va. bituminous coals to carbon dioxide were measured as functions of water saturation and structural orientation at simulated overburden pressures of 200 psig and 400 psig. The results indicate that carbon dioxide has a negligible effect on permeability reduction. This fact is of interest to both in-situ coal gasification and to methane drainage. Reductions in permeability were of the order of 0 to 20 percent of values determined with nitrogen. The effect of CO/sub 2/ on the Gillette coals was to drastically alter the shape of the effective and relative permeability curves at lower water saturations. The effect of doubling the overburden pressure had a proportionally inverse effect on the effective permeabilities to gas. This effect is most pronounced at lower water saturations. The general characteristic behavior of the relative permeability curves remained relatively independent of the stress field.