The paper presents the results of an experimental investigation aimed at characterising the water and air permeability properties of low-permeability claystone formations from a Mesozoic sequence in Northern Switzerland. The experiments, besides providing quantitative data to calibrate hydraulic and two-phase flow properties, intend to analyse the phenomena and processes, which control the percolation of air through an initially water saturated claystone. Fast controlled-volume rate air injection experiments were performed in a triaxial cell, testing a total of four rock samples under isotropic stress state conditions at different initial porosity and at two sample orientations (flow parallel and orthogonal to bedding planes). Simulation results showed a good agreement between the measured pressures at the injection and outflow sides of the sample using a standard two-phase flow simulation code.