A new technique is described for studying the existence of a thick viscous lubricant film adjacent to the surface of a metal. It uses mercury instead of a solid plate to displace a hydrocarbon from the metal surface, thereby avoiding spurious effects due to dirt or surface asperities. The capacitance between the solid metal and the mercury is used to indicate the film thickness. A special circuit enables the potential difference applied to the surfaces to be reduced to the order of microvolts. A thick film is formed when there is a surfactant present in the hydrocarbon which reacts chemically with the metal. The soap so formed appears to enmesh the hydrocarbon near the surface, forming a grease layer some 103–104Å thick. Preliminary results show the effect of carrier and surfactant matching.