Lubricant plays a vital role in reducing wear, friction and energy consumption in any machinery. It is mainly used in automotive, industrial, processing, and marine. Various types of lubricant were developed from time to time to meet with the market requirement. However, lubricant performance demanded by market changes as the application varies. For instance, lubricant with high thermal stability is required in drilling, which is High Temperature High Pressure (HPHT) condition. Recent studies have revealed that by adding an optimum concentration of nanoparticles into lubricant, the tribological performance of the lubricant can be improved significantly. Viscosity of lubricant is vital in terms of forming lubricating film and reduces friction. In this study, mutliwalled carbon nanotubes were added to lubricants through hydrodynamic and acoustic cavitation. The results indicated that addition of multiwalled CNT definitely improve nanofluids' viscosity. Besides, comparison between methods of preparation showed that hydrodynamic cavitation alone yield best suspension with highest viscosity in both 25 ppm and 100 ppm cases. © 2016 The Authors.