Surface and volume flow have been studied in a microporous carbon membrane of high surface area for He, Ar, N$_2$, Kr and CO$_2$ and for the mixtures Kr + N$_2$ and CO$_2$ + Kr. Although the adsorption extended beyond the range in which Henry's law was valid, the permeability coefficient, K, remained independent of amount sorbed and isotherm curvature. For a given gas the permeability coefficient was also identical for the pure gas and for the gas in binary mixtures in which competitive adsorption was occurring. These results indicate that, in the range investigated, surface flow occurred by a random walk diffusion mechanism (surface hopping), rather than by a viscous flow mechanism. The products K$\surd$M (M denoting molecular weight) show smooth correlations with parameters determining the adsorbability of the flowing gases.