A study of the rheological properties of lubricating oils was made by means of semiquantitative measurements of the viscosity and elasticity of surface and interfacial films. A torsion‐pendulum type, surface viscometer was used. A refined, uncompounded mineral oil was shown to possess neither surface nor interfacial viscosity or elasticity. One additive in mineral oil showed surface viscosity and elasticity, and two additives developed these properties at an oil‐water interface. The aged, viscous surface and interfacial films studied were found to be non‐Newtonian.