A new technique using mercury porosimetry to characterize the percolation properties of porous media over several different length scales has been presented. The methodology employed a new theoretical model of a porous medium. The model may be used to represent a highly heterogeneous, porous material, with a wide pore-size distribution, over a broad range of length scales from similar to4 nm to 0.01 m. The characteristic statistical parameters which defined the model were obtained from mercury porosimetry scanning loop and miniloop experiments. Mercury porosimetry miniloops have been shown to give rise to so-called "miniloop spectra". These spectra describe the variation of the value of a characteristic mercury entrapment function with pore size. The shapes of these spectra have been found to be sensitive to both the form of the pore-size probability density function and the pattern of the spatial geometric arrangement of pore sizes in the void space. Additional, complementary information on the pore structure was provided from nitrogen sorption and magnetic resonance imaging in order to eliminate ambiguities in the interpretation of the mercury porosimetry data. The overall approach can be considered as a methodology for pore structure tomography using mercury porosimetry and nitrogen sorption.