The ideal 2-state model is exclusively used for describing the liquid phase in 3 rd generation CALPHAD work. However, not all types of liquids can be described using an ideal 2-state model and for liquids qualified as fragile, a regular 2-state model appears to be a more promising modelling solution. The formalism and phase diagram of the regular model are presented with particular emphasis on the pressure variable. The main characteristics of the regular 2-state model are illustrated through a parametric study and the two test cases of tellurium and water taken from literature studies. The present article suggests that, compared to its ideal counterpart, the regular 2-state model may represent a valuable complementary modeling tool that considerably broadens the spectrum of phenomena that can be described. This model should only be used if it significantly improves the description compared to the ideal model, and its applicability in a multicomponent system should also be verified.