We measured the electrical impedances of 22 sandstone samples during oil‐driving‐water tests using the two‐electrode method. Experiments show that the imaginary part X of the impedance (R + iX) of rock may respond well to water saturation in the frequency range 100 Hz–15 MHz. We found that the maximum −X values and their corresponding interfacial polarization frequencies are linear with water saturation. The lower critical frequency is found to vary with water saturation, in an unclear relationship with the characteristic length of rock. The dissipation factor at the interfacial polarization frequency remains quite stable and may be an indicator of the pore structure of rock. We used an equivalent circuit to explain the dispersive behavior of rock. More than one interfacial polarization frequency in the impedance Argand plot is predicted and can be observed if the measurement frequency range is wide enough.