Examination of viscosities for fluids in the system H2O-NaCl predicted by the commonly-used model of Palliser and McKibbin has identified regions of pressure-temperature-salinity (PTx) space in which the model delivers values that are inconsistent with some experimental data and exhibits discontinuities and trends that are unexpected. Here, we describe a revised empirical model to calculate viscosity of H2O-NaCl fluids that shows good correlation with experimental values and shows trends that are consistent with known or expected behavior outside of the region where experimental data are available. The model described here is valid over the temperature range from the H2O solidus (similar to 0 degrees C) to 1000 degrees C, from similar to 0.1 MPa to <= 500 MPa, and for salinities from 0 to 100 wt % NaCl. (C) 2016 Elsevier B.V. All rights reserved.