The viscosity models of pentafluoroethane (R125), 1,1-difluoroethane (R152a), 1,1,1,2-tetrafluoroethane (R134a), difluoromethane (R32), and 1, 1, 1-trifluoroethane (R143a) have been correlated using the friction theory in conjunction with the Span-Wagner equation of state and Sato et al. equation of state. The obtained viscosity models cover a wide range of fluids states, including the supercritical region. And, the models can represent the viscosities of the studied refrigerants to within or close to the uncertainty of the selected primary experimental data. It is apparent that this model is satisfactory and appropriate for most industrial applications. At the same time, the dilute gas viscosity has been correlated using only two constants for each refrigerant, and the results have an agreement with the uncertainty of the recommended data. (c) 2007 Elsevier B.V. All rights reserved.