A viscosity model based on the similarity between PvT and T mu(viscosity)P relationships for a better description of viscosity has been developed based on Peng-Robinson (PR) cubic equation of state (EOS). The model is able to calculate viscosities of pure or mixed light hydrocarbons with better accuracy. At a saturated state, when the temperature is specified, the PR EOS with Twu's alpha-function is applied to predict the saturated vapor pressure. Then the saturated liquid and vapor viscosities of pure hydrocarbons can be calculated based on the new viscosity model with the specified temperature and pressure. The new viscosity model is applicable to describe viscosity of hydrocarbons in the near-critical region with a smooth transition like PR EOS for density. (c) 2006 Elsevier B.V. All rights reserved.