The densities of the Argonne Premium Coal samples were measured using H-2, He, and a H-2-He mixture (49.13 vol % of H-2 in He) in a gas pycnometer. Significant differences between the apparent hydrogen densities and helium densities were observed. The larger H-2 densities observed in the tests are attributed to H-2 gas adsorption/absorption on coal. The H-2 gas adsorption coefficient increases with increasing carbon content. The "true" or intrinsic densities of coals extrapolated from plots of the measured density versus H-2 gas partial pressure are very close to the He-densities. The organic coal density (dmmf coal density) was obtained after a correction for the mineral matter in the coals. It decreases with increasing carbon content initially, reaches a minimum at about 82 wt % carbon, and then increases with increasing carbon content.