The critical temperature of ionic liquids is predicted by scaling-law, Guggenheim, and Eotvos approaches using surface tension data measured in the temperature range of 293-393 K The available surface tension data for imidazolium-, phosphonium-, and ammonium-based ionic liquids, with different anions content show that the predicted critical temperature is a function of cation type and its alkyl chain length as well as the anion type According to this dependence on the nature of the ionic liquid, the anion-cation interaction energy (E-inter) was calculated by quantum mechanical density functional theory and the correlation with the predicted critical temperature was studied The predicted critical temperature has a direct correlation to the absolute value of E-inter The ionic liquids with the BF4- anion, which consistently have the highest critical point temperature, also have the largest absolute value of E-inter As the alkyl chain length increases, the critical temperature decreases When the surface tension is measured under a liquid-vapor equilibrium, the prediction has the meaningful feature of producing the critical-point temperature