The reliability of combustion engines is enhanced by lubrication, which provides wear protection along with reduced emissions and fuel consumption through the minimisation of friction. Organic Friction Modifiers (OFMs) are a class of friction-reducing engine oil additives, which are known to adsorb at metal surfaces. However, the mode-of-action by which OFMs operate has yet to be clearly defined. To understand how these additives function, a novel tribometer rig has been developed which enables neutron reflectivity experiments to be carried out at elevated temperatures and pressures, whilst the surface is sheared. In this set of experiments, we will measure the thickness of the film formed by glycerol mono oleate on iron oxide surfaces as a function of concentration and shear.