The new apparatus described enables making simultaneously absolute measurements of physisorption, bulk density, and adsorption kinetics of multicomponent gas mixtures as a function of pressure up to 30 MPa. The method which combines the dynamic and the gravimetric methods is self‐sufficient because it does not require complementary data. An in‐line high‐pressure chromatographic device directly measures the time evolution of the effluent flow composition (breakthrough curves). Results of adsorption, density, and adsorption kinetics at high pressures of the equimolar Ar‐CH4mixture on activated carbon are reported.