Nanofluids, as a kind of new engineering material consisting of nanometer-sized additives and base fluids, have attracted great attention of investigators for its superior thermal properties and many potential applications. Many investigations on nanofluids were reported and especially some interesting phenomena, new experimental results and theoretical study on nanofluids, in which consistent and inconsistent even contrary conclusions were reported, have been presented in literature. The aim of this review is to summarize recent development in research on synthesis and characterization of stationary nanofluids and try to find some challenging issues that need to be solved for future research. (c) 2009 Elsevier B.V. All rights reserved.