Permeability of natural materials as a physical process is of fair importance in many fields. It has been characterized by a laboratory test whose application in evaluation of in situ situation, however, requires knowledge of more detailed relations for a given couple fluid/solid matter. The proposed grant project is aimed to extension of predicating ability of the test with other physical quantities, namely with direct correlation with textural parameters. A pore group active for permeability will be identified, their mean equivalent radius and Reynold s number determined. For gases, effect of molecular size, of density and viscosity will be investigated, for fluids also effect of interphase forces, surface tension and adhesion. Relation between the absolute (single-phase flow) and the relative permeability (two phase-flow) will be described. Data obtained for model substances will be applied for gas-bearing coals as gas collectors and smectite rich clays as impermeable barrier.