Four different methods (Prausnitz, Won, Hansen and Salim) that can be used to calculate phase equilibria involving a solid phase, are described. Improved versions of these methods (Ungerer, Chung, Erickson and Brown) are discussed as well. The model proposed by Prausnitz (Prausnitz et al., 1986), can be applied to calculate solid-liquid phase equilibria assuming that different solid forming components do not form a solid solution. The models proposed by Won (1986), Hansen (Hansen et al., 1988) and Salim (Salim et al., 1994) can be used to calculate vapour-liquid-solid wax phase equilibria for paraffinic hydrocarbon mixtures. The model proposed by Salim has the advantage that only one equation of state is used to calculate the entire phase diagram, whereas the other models have to be used in combination with an equation of state to calculate the liquid-vapour equilibrium. Modifications for the model, originally given by Prausnitz, were proposed to describe the influence of the pressure and to include the possibility of solid-solid transitions (Ungerer et al., 1994). Ungerer used a simplification of this model, to reproduce crystallisation in four synthetic gas condensate mixtures, achieving good agreement with experimental data. Gas-solid equilibria, are adequately described with a negative slope of the gas/gas-solid transition curve in the P, T diagram, which seems to be characteristic of solid forming gas condensates at high pressure, above the dew point curve. Chung (1992) proposed a method based on Won's model, with improved predictions for the wax appearance points (W APs). This model was used to calculate W APs for three North Sea crudes, showing good agreement with measured temperatures. The quantity and composition of the precipitated wax can also be calculated but accurate experimental data are scarce, since waxy crystals entrap significant amounts of liquid hydrocarbons. Alphaltene solubilities in organic solvents and oils can be accurately predicted. For highly polar or associating solvents, however, the model is inadequate and the activity coefficient of the solid in the liquid phase has to be predicted by other methods such as group contribution methods. Erickson (Erickson et al., 1993) proposed modifications for the model described by Won, to obtain a better fit with experimental data. The model does not take into account the influence of the pressure, the difference in molar heat capacity between the solid and the liquid phase and assumes unity for the ratio of activity coefficients between the liquid and the solid phase. The model was used to predict WAPs and the amount of wax formed as function of the temperature, for 16 real crudes and condensates, using only a compositional analysis and no tuning parameters. It provided excellent predictions of the W APs, as well as a good qualitative agreement for the solid wax content. Since the model does not need to be tuned to individual crudes, the mixing of crudes, solvents and condensates can easily be included in the model. This model also provides an excellent method for predicting solid-liquid­vapour phase behaviour for hydrocarbon systems, based solely upon detailed compositional analysis... - Jaartal geschat