The subject of fluid permeation through porous media has been invoked as a basis for the study of gas and liquid leakage through fibrous gasket materials. The study has encompassed a variety of annular specimen sizes, specimen porosities and structures, fluid viscosities, and fluid pressure. To provide some control of material properties, the ASTM F37 Method B test method was modified to incorporate shims in the fixture. This modification prevents material creep during the test and provides a known porosity for each leakage measurement. The resulting data is highly reproducible and can be related to the intrinsic pore structure of the tested material. The technique can be utilized as a means to study the pore structure for purposes of optimizing gasket formulations; conversely, from a knowledge of the structure the leakage rate can be predicted as a function of sample geometry, state of compression, fluid viscosity, and fluid pressure.