Nanometric silver dispersed water based nanofluids have been prepared by a single-step chemical process. The crystallite/particle size, morphology and purity of nanoparticles were characterized using standard microscopic, diffraction and spectroscopic techniques. The thermal conductivity enhancement (with respect to the base fluid) has been determined as a function of concentration and size of silver particles using transient hot-wire technique. The accurate fitting of the experimental data of thermal conductivity enhancement with a theoretical model developed by Patel et al. [24] predicts that high specific surface area of the particles, layering at the liquid-solid interface and Brownian motion may be responsible for enhancement. (C) 2011 Elsevier Inc. All rights reserved.