An extensive experimental evaluation of electrical conductivity of nanofluids containing metallic and ceramic particles (Cu, Al2O3, and CuO) with different volume fractions in the dilute regime, particle sizes, electrolyte effect, temperature and base fluids has been carried out. It is observed that, in both water- and ethylene glycol (EG)-based nanofluids, the electrical conductivity increases with increasing particle concentration and reducing particle size. It is argued that the effective dielectric constant and density are at the root of the counterintuitive observation that the electrical conductivity enhancement of ceramic nanofluids is more than that of metal-based ones which is substantiated by the Clausius-Mossotti relation for the polar fluids. The influence of surfactant is found to increase the stability and decrease the electrical conductivity of the nanofluids by increasing its viscosity. There is a rise in electrical conductivity of nanofluids having low electrolyte concentration whereas a decrement is observed in nanofluids of high electrolyte concentration due to reduced surface conductance. These experimental observations on alumina nanofluids are compared with the theoretical model proposed by O'Brien  for electrical conductivity of dilute suspensions. It has also been observed that there is no significant effect of fluid temperature on the electrical conductivity in the range 30-60°C. This clearly indicates that enhancement mechanism for electrical conductivity is completely different from that of thermal conductivity in nanofluids. © 2012 Elsevier B.V.