A technique is described for characterizing the response behaviour of nernstian gas sensors to sinusoidal pressure modulation in the frequency range 0.1-1000 Hz. Relaxation times down to 0.2 ms could be resolved for first-order kinetics. For ceria-based oxygen sensors the shape of the spectra indicated diffusion-controlled kinetics and provided additional information when compared with electrochemical impedance spectra. Fast relaxation times down to 2.5 ms were found at 1173 K in air for Pt electrodes. The pressure modulation technique avoided corrosion effects which might be induced by alternating currents and thus made it possible to characterize the kinetics of carbonate-based CO2 sensors. Relaxation times were determined down to 4.5 ms at 973 K in air for Pd electrodes.