A method for the measurement of entrapped gas as a means of investigation of the unsaturated flow phenomena consists of two simultaneous measurements made with an apparatus combining an air-pycnometer to obtain the volume of the free gas phase and a pressure cell with which the water outflow or inflow volume is measured. By difference the volume of entrapped gas is calculated. Results obtained on glass beads show that gas entrapment occurs mainly during the wetting of the sample, reaching a maximum entrapped gas content of about 6% of the total sample volume. The possibilities offered by the method are similar to those of the pressure cell, with the advantage that the amount of entrapped gas is known. Consequently, the influence of entrapped gas on capillary conductivity and water diffusivity can be investigated in drainage and infiltration studies.