Non-invasive x-ray computed tomography has been used to investigate the pattern of infusion of inert gas (xenon) into coal. The access of gas to the internal surfaces of coal and char has important consequences for reactivity towards liquefaction and gasification. The pattern of infusion is very nonuniform with gas penetrating along the bedding planes at a faster rate than across them. Deconvolution of the digital data from a sequence of images yields an effective diffusion or constant across a mainly vitrinite band of 1 x 10/sup -6/ cm/sup 2/sec/sup -1/. 38 figs.