Abstract Fatty acids constitute an important group of chemicals with extensive end-use markets, either for their direct uses or for the intermediate uses of their numerous derivatives. These oleochemical products are currently purified or fractionated using distillation at subatomspheric pressures. Due to the increasing interest of the pharmaceutical industry in some fatty acids with high purity, supercritical fluid extraction followed by appropriate fractionation steps are also employed. It would therefore be convenient to utilize a single thermodynamic model that is capable of predicting all thermodynamic properties needed, and covering the whole pressure range which is currently applied in both industries. Different equations of state and activity coefficient models were scanned, and the perturbed hard chain equation of state (PHC-EOS) provided results which are as good as those obtained using activity coefficient models, and in some cases better. Since there are very scarce experimental data on the be...