This work aims to draw a more fundamental understanding of the rheology of nanofluids and the interpretation of the discrepancy in the literature. The rheology of dispersions based on SiO2 and Al2O3 nanoparticles obtained by four different methods is experimentally investigated in the Newtonian range. It is shown that the viscosity dependence on concentration for nanofluids with particles of different synthesis methods has different values. The parameter of the associated liquid layer model describing the intensity of particles and dispersed medium interaction, as well as the ζ-potential of these liquids, were determined. The correlation between the ζ-potential and the thickness of the associated liquid layer is shown, and the possibility of their use for predicting the behavior of nanofluids is discussed.