A new corresponding states model for predicting the viscosity of heavy crude oils and petroleum fractions is proposed in this work. The model uses decane and eicosane as reference components for petroleum fractions of average molecular weight higher than 142. The viscosity of a component-or fraction may be obtained from the viscosities of these two reference fluids (decane and eicosane) at the same reduced temperature and reduced pressure using the molecular weight as an interpolation parameter. This model showed better accuracy in predicting the viscosity than the model that uses one reference (methane) or two references (methane and decane), when the molecular weight is higher than 142. The present model, when tested on 187 data points for 29 undefined heavy petroleum fractions from 15 worldwide crudes, yielded an overall deviation of 5.3%. Testing of the model on 53 data points for seven crude oils from offshore Abu Dhabi yielded an average absolute deviation of 5.9%.