A new volumetric frequency response (VFR) system was developed for studying the mass transfer characteristics of gases in microporous adsorbents. For this VFR system, the differential pressure response from a small perturbation in volume was measured in a closed system after equilibrium was established for a gas adsorbate-adsorbent pair at constant temperature and pressure. It operates over a wide range of frequencies from 10(-5) to 10 Hz, from atmospheric pressure down to vacuum pressures of 100 Torr, and at temperatures from 5 to 80 degrees C. The sample chamber holds up to 100 g of adsorbent. These operating ranges make this new VFR system capable of measuring mass transfer characteristics of adsorbate-adsorbent systems at conditions relevant to many commercial separation processes using a relatively large volume of adsorbent in a unique packed bed arrangement. The apparatus and procedure were described in detail, including the use of runs with different gases and different porous and nonporous solid beads and pellets to fully characterize the system in terms of its dynamic behavior especially at high frequencies and in terms of various volumes required in the analyses. It was shown how to analyze these baseline runs to correct for gas compression heating and pressure drop effects in the high frequency region of the pressure change amplitude response curves and to determine intensity (or amplitude ratio) and phase shift (or lag) response curves from which fundamental thermodynamic and kinetic information for an adsorbate-adsorbent pair could be extracted. To demonstrate the utility of this new VFR system, experiments were carried out with CO2 in 13X zeolite beads at 25 degrees C and 100, 200, and 760 Torr using 32 frequencies at each pressure. Slopes of this isotherm estimated from the intensity response curves at low frequency showed very good agreement with those measured independently. The mass transfer time constant estimated from the maximum in the phase lag response curve also agreed well with that reported in the literature. Unique features of the intensity and phase lag response curves were revealed.