In this paper we present a complex admittance analysis of three electrode systems when exposed to aqueous KCl solutions: uncoated gold, gold/alkyl mercaptan and gold/alkyl mercaptan/22-tricosenoic acid Langmuir - Blodgett film. For each arrangement, the experimental data were fitted to the theoretical responses of equivalent electrical networks of capacitors and resistors. For the first two electrodes, a simple model consisting of an electrolyte resistance in series with the Gouy - Chapman diffuse layer capacitance described the experimental data well. For the third system, incorporating the high-impedance bilayer of 22-tricosenoic acid, a more complex equivalent circuit was needed. The physical interpretation of its components is discussed. In all cases universal capacitors with a power-law frequency response had to be used to model the real systems accurately.