An electric submersible motor is provided that includes a plurality of rotors and bearings mounted on a shaft, and a stator external to said rotors. A running clearance is located between an inner diameter of the stator and external diameter of the rotors, and includes a lubricating oil that includes a base hydrocarbon oil and a plurality of nanoparticles. Also provided is an improved lubricant oil and method of preparation thereof are provided. The lubricant oil includes a hydrocarbon containing base oil and a plurality of nanoparticles. The nanoparticles may be present in an amount up to 30% by volume.