A high-resolution slow wave imaging system based on attenuation measurement of transmitted airborne ultrasonic waves was developed to study the inhomogeneous pore structure in permeable formations. Currently, the threshold sensitivity of our system is approximately 100 mD, making possible the characterization of typical petroleum reservoir rocks with spatial resolution of between 0.5 and 5 mm in the 50 kHz to 500 kHz frequency range. The degree of disorder in permeable solids is of crucial importance especially when the relative permeability is considered. It is expected that this new technique can complement such methods as hydrodynamic dispersion measurements and petrography for characterizing flow in porous rocks. ¿ American Geophysical Union 1995