The general one-parameter friction theory (f-theory) models have been further extended to the prediction of the viscosity of real "live" reservoir fluids based on viscosity measurements of the "dead" oil and the compositional information of the live fluid. This work representation of the viscosity of real fluids is obtained by a simple one-parameter tuning of a linear equation derived from a general one-parameter f-theory model. Further, this is achieved using simple cubic equations of state (EOS), such as the Peng-Robinson (PR) EOS or the Soave-Redlich-Kwong (SRK) EOS, which are commonly used within the oil industry. In sake of completeness, this work also presents a simple characterization procedure which is based on compositional information of an oil sample. This procedure provides a method for characterizing an oil into a number of compound groups along with the critical constants and parameters that are required by an EOS. The resulting EOS characterized fluid correctly reproduces properties such as the saturation pressure and the liquid phase density, from reservoir conditions to low pressure conditions. The viscosity modeling approach along with the characterization method presented in this work provide a complete self-consistent procedure for the viscosity and density modeling of reservoir fluids. (C) 2003 Elsevier B.V. All rights reserved.