The temperature-dependence of the viscosity η of a liquid can be described by means of an empirical equation suggested as early as 1921 byVogel: η=A exp.B/(T−T 0), which, besides the temperatureT, contains three adjustable structuredependent parametersA, B andT 0. An equation of the same form is suited for describing the temperature dependence of the most probable relaxation timeτ m in polymers, and can be easily transformed into the socalled WLF-equation, because the empirical parametersB andT 0 are simple functions of the WLF parameters. In many cases, the temperature-dependence of such quantities as mechanical or dielectric relaxation times, viscosities, diffusion coefficients etc, is regarded as a consequence of a thermal activation process ruled by a temperature-dependentGibbs Free Energy of activationΔG. On the basis of this concept both parametersB andT 0, can be related to the more fundamental high temperature limiting value of the activation energyΔH and the parameterT 0 to the temperature at whichΔG becomes infinite. The parameterA is normally taken to be temperature-independent; theoretically, however, it may just as well be temperature-dependent. Although it is difficult to decide from experimental evidence whether this is the case (accurate values over a large temperature range must be available), one should realize that analysis done by means of a temperature-independent pre-exponential factor gives a set of values for the parameters which differ greatly from those found when e.g.A is set proportional toT −1 orT −2. Literature values for the viscosities ofn-paraffins have been statistically analysed. It is concluded that η in theVogel-equation had better be replaced byη T 1.2/ϱ, whereϱ is the density of the liquid. Values are given for the modifiedVogel, WLF and activation parameters of the paraffins and ethylenecopolymers, those for the latter being obtained from our own dielectricτ m measurements. By analogy,τ m would then have to be replaced byτ m T 2.2. However with our dielectric data, such a refinement would not give any great improvement.