Indopol H-8, provided by INEOS (London, UK), was used as the base oil for of the tribometer experiments in this study. This is a poly(butene) oligomer with an average molecular weight, Mn = 490 g mol -1 (degree of polymerisation ≈ 4) and a polydispersity index, Mw/Mn = 1.85. EHL fluid film thickness is determined by the lubricant viscosity at the inlet, where pressure is relatively low (~100 MPa). At ambient pressure, Indopol H-8 has a kinematic viscosity of 15 cSt at 100 °C, which is similar to the low-molecular weight poly(isobutene) (14 cSt at 100 °C), but much higher than the base oil (6 cSt at 100 °C) poly(α-olefin) (PAO6) and traction fluid (4 cSt at 100 °C) 2,3-