Experimental study has been carried out to determine the thermal conductivity of five different nanofluids containing aluminum oxide, copper oxide, zinc oxide, silicon dioxide and titanium dioxide nanoparticles dispersed in a base fluid of 60:40 (by mass) propylene glycol and water mixture. The effect of particle volumetric concentration up to 6% was studied with temperatures ranging from -30 to 90 degrees C. Experiments showed an increase in thermal conductivity of nanofluids with increasing concentration and temperature. The thermal conductivity of nanofluids showed a strong dependence on particle volumetric concentration, particle size, properties of particles and the base fluid and temperature. Several existing theoretical models for thermal conductivity of nanofluids were compared with the experimental data, but they all showed disagreement. From comparisons, the most agreeable model was selected and a curve-fit constant was derived to match the data of propylene glycol nanofluids. This model expresses the thermal conductivity of nanofluids as a function of Brownian motion, Biot number, fluid temperature, particle volumetric concentration, and the properties of the nanoparticles and the base fluid. This model provided good agreement with 600 experimental data points obtained from five different nanofluids with an average absolute deviation of 1.79 percent. Because of the enhanced thermal conductivity with increasing temperature, nanofluids should be more beneficial at higher temperature applications. (C) 2016 Elsevier Ltd. All rights reserved.