The model of Xuan et al. (2003) for the thermal conductivity of nanofluids in which Brownian motion effect is added to the classical Maxwell's equation is discussed. The model is revised. Also, a different model is given and found to yield the same expression for the effective thermal conductivity after amending Xuan et al.'s model. The findings do not support the claim that Brownian motion of nanoparticles has a significant impact on thermal conductivity. Also, nanoparticles clustering is found to have a very minor effect on the effective thermal conductivity of nanofluids; however, the analysis may not be appropriate to draw conclusions about the impact of clustering. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2368-2369, 2015