A relationship is identified between the effective carbon number (ECN) and parameter b in the one-parameter viscosity equation : log (mu + 0.8) = 100 (0.017)b. The generalized correlation, b = -5.745 + 0.616 In (ECN) - 40.468 (ECN)-1.5, provides an equation to predict parameter b, which gives values that are within the maximum deviation of 5 % for ECN < 10 and 1% for 10 < ECN < 44 of the empirically-determined values for 70 liquid hydrocarbons. The calculated viscosities are within 5% of literature data. The viscosity prediction method is simple to use, and it can be extrapolated reliably to heavier hydrocarbons.