This paper results from an ongoing investigation into modelling the thermal conductivity for alumina-water nanofluids. Seven existing theoretical and empirical models for thermal conductivity of nanofluids have been evaluated for their accuracy by comparing the predicted versus experimental data for a wide range of test conditions. The existing models were found to provide inaccuracies (over/under-predictions) in the range of 2.34-58%. A new model has been developed by employing Prandtl. Reynolds and Brinkman numbers, representing the effects of micro-convection, localized turbulence and the ratio of heat transfer by diffusion to conduction for particle and fluids on the thermal conductivity of nanofluids. Evaluation of the new developed model by comparing the predicted results against experimental data revealed that the new model is within 5% accuracy for a wide range of data. (C) 2012 Elsevier B.V. All rights reserved.