We develop an experimental technique that uses computed tomography (CT) scanning to provide high-resolution measurements of aperture distribution and in situ saturation along with capillary pressure and relative permeability for the same rough-walled fracture. We apply this technique to an induced fracture in a cylindrical basalt core undergoing water drainage. We find that the sum of the water and gas relative permeabilities is much <1 at intermediate saturations and the water relative permeability shows a sharp change over a narrow range of average water saturation. In situ saturation maps show channeling of gas and significant retention of the wetting phase (water). The capillary pressure initially increased and then decreased with decreasing water saturation. Although this type of capillary behavior is atypical for unsaturated flows, we find that the sizes of the gas-filled apertures are consistent with the measured capillary pressure. ¿ 2001 American Geophysical Union