Abstract Helium, Hg, methanol, water and CO 2 were used as probes at 298 K to characterize densities, porosities and surface areas of coal macerals. Densities, measured by He and Hg displacement, permit the determination of maximum open pore volumes in macerals in the absence of significant imbibing of the fluids within the coal structure. Densities measured in methanol, water and CO 2 are frequently greater than those measured in He both because of their penetration into pores closed to He and into the coal structure due to imbibing. Imbibing into the coal structure results in the swelling of macerals, the extent of which is strongly rank dependent. Uptake of CO 2 on macerals is large. It is concluded that it is due primarily to pore filling (coverage of micropores) and not to penetration within the coal structure. Coverage of micropores by water is only a fraction of that found for CO 2. From this it is concluded that only a fraction of the surface of coal macerals is composed of hydrophilic sites.