In recent years, along with ever increasing load demand, penetration of renewable energies has put additional stresses on transformers leading to poor efficiency and reduced lifetime. Hence, the efficient thermal management added with higher dielectric breakdown strength (DBS) of the transformer oil (TO) is the call of the day. “Nanotechnology,” may be a game changer in this issue. Thus, nanofluidic TO has become a promising replacement for liquid dielectrics and an emerging field of research in the global perspective. This chapter explores the road map of the research work carried out in the last two decades since the inception of mineral oil based nanodielectric fluids (NDFs). A comprehensive review on a pool of nanofillers with different sizes, morphologies, filler-fraction, aspect-ratio, conductivities, relative permittivity, and thermo-physical properties reported in the literature to improve the efficacy of TO have been systematically addressed. The impact of materials chosen, their parametric variation, shortcomings, and mechanisms have been clearly explained in alerting dielectric breakdown strength, resistivity, and thermophysical properties such as thermal conductivity, stability, and viscosity of TO. Growing trend in the dispersion of multiple nanofillers, the use of 2D nano-structures, and tailor-made nano-composite have been observed in this review. This chapter also encompasses the prospects of environment friendly alternative oils as liquid insulation and impact of nanofillers on improvement of their electrical and thermophysical properties. Finally, the challenges and opportunity in the domain of nanofillers associated with nano engineered TO have been furnished, targeted towards smart, futuristic, and stable insulating nano-coolants development.