A new five-parameter corresponding states model has been developed for viscosity and proton spin-lattice relaxation rate applicable to a variety of hydrocarbons in the dense fluid phase region. This model is the key to the development of unprecedented, accurate correlations between the proton spin-lattice relaxation rate, R\sb1, and the viscosity, η, of pure hydrocarbons, with an observed root-mean-square deviations of less than 8.0%. For hydrocarbon mixtures, the notion of "effective" spin-lattice relaxation rate, introduced by Zega et al\sp1,2, is pursued. Then, simple mixing rules are successfully applied to extend the model to mixtures. The four-parameter corresponding states treatment, utilizing the shape factors as proposed by Leach and Leland\sp3, yields correlations of comparable accuracy, when confined to long-chain alkanes.