The paper herein proposes a method to simultaneously measure the friction, wear, and thickness of boundary films under a pure sliding contact between metallic surfaces. The method is based on the capacitance method used by Crook and Dyson et al. to measure elastohydrodynamic film thicknesses. Pilot tests conducted on sunflower oil using the new method showed an appreciable growth in the boundary film thickness, with a corresponding drop in the coefficient of friction. Very little wear was observed during the film growth. It is postulated that this growth was due to the polymerization of the unsaturated fatty acid chains.