The relation between capillary pressure (P _c ) and interfacial area has been investigated by measuring P _c and the electric permittivity at 100 kHz simultaneously as function of the water saturation, (S _w ). Drainage and imbibition experiments have been conducted for sand-distilled water-gas (CO₂/N₂) systems. The main capillary cycles and the scanning curves show hysteresis with the drainage curves displaying higher values than the imbibition curves. The 100 kHz permittivity data also show hysteresis between drainage and imbibition. Furthermore non-monotonic behavior is observed, which is analogous to the interfacial area characteristics obtained from network and micro-pore models. The permittivity behavior is attributed to polarization of the gas-water and water-solid interfaces. The permittivity hysteresis is provoked by the different phase distributions and geometries. Our results show that P _c is a unique function of the permittivity and S _w , and therefore this work provides clear evidence that the permittivity is a measure for the interfacial area.