This is important since it is here that the friction behaviour depends strongly on the OFM concentration and consequently the coverage. Ambient temperature (300 K) was used and each test was conducted for 1 h to reach steady state friction. The friction coefficient was measured for pure base oil and for OFM concentrations between 10 -6 M and 0.02 M, for a total number of 7 HFRR tests. At the beginning of each test and once the contact was flooded, the ball and disc were held stationary and no pressure was applied during 5 minutes to allow for the formation of the OFM film, which is similar to the procedure used by Fry et al. The two specimens were cleaned prior to each test with acetone and toluene.