A twin disk rig was used to perform a series of experiments investigating mixed lubrication. The disks used in the experiments were manufactured from case carburising steel, were hardened and had a surface finish ground transverse to the direction of oil entrainment in order to simulate the roughness orientation typically found on involute gear teeth. Roughness profile measurements were taken in-situ between experiments which showed that the initial phase of operation for as-manufactured surfaces is a period of rapid plastic deformation, where asperity features on the surfaces accommodate to one another. It was found that this reduction in roughness improved the state of lubrication by reducing instances of contact between the surfaces. Contact was assessed by measuring the electrical contact resistance between the disks during the experiments and the level of the contact voltage between the disks was used as an indicator of the state of lubrication existing between them. It was found that variations in the dimensionless film thickness strongly influenced the level of the contact voltage. The contact voltage waveform was also found to exhibit similarity between revolutions, indicating repeated contact between groups of interacting asperities. Realigned profile traces demonstrate that prominent asperity features undergo significant plastic deformation during the running-in process. Over extended operation, it was seen that these same roughness features can be subject to a degree of fatigue at the roughness scale, which has been identified as micropitting failure in the experiments. Modifications to an existing numerical model simulating the isothermal non-Newtonian EHL point contact to enable the use of measured 3D roughness shows that high pressures are generated in the region of interacting asperity features. Asperity contact is also seen to occur across the length of prominent ridges in agreement with images obtained from 3D profilometry which demonstrate prominent ridges experiencing fatigue.