This area concerns the modeling of phase equilibria and mixing enthalpies in complex systems, particularly those involving petroleum fluids. Oil companies need to know, when operating a well, whether the fluid they are going to extract is oil or gas, which largely conditions the taxes they will have to pay, as well as the duration of the well's operation. Phase equilibrium curves provide access to this kind of information.

It is therefore crucial for these companies to have models for predicting phase equilibria, including light compounds (methane, CO2, N2, H2S...) and heavy hydrocarbons (alkanes, cycloalkanes, naphthenes, aromatics). These models need to be predictive, sufficiently accurate and enable rapid calculations. In addition, since the abandonment of oil platforms, as the seawater is no longer separated from the oil fluid on the platform, the exploitation of offshore oil deposits has raised a new problem: the formation of hydrocarbon hydrate "plugs" preventing the subsea routing of the water-oil mixture; to prevent this formation, an inhibitor, generally methanol or a glycol, is added to the mixture. The phase equilibria to be predicted are then much more complicated, since both liquid-vapor (VLE) and liquid-liquid (LLE) equilibria must be represented simultaneously.