A thermodynamic model to predict wax formation and the low-temperature phase behavior of different types of fuel is proposed. The model is based on an accurate description of the nonideality of the phases in equilibrium using modified UNIFAC for the liquid phase and the UNIQUAC equation for the description of the solid phase, A comparison of the model predictions with literature data for the low-temperature behavior of a number of jet fuels, ship propulsion distillate fuels, and diesel fuels is presented to validate the model. It is shown that it provides an excellent description of both the composition of the phases in equilibrium and the fraction of solids in partly crystallized fuels, for all types of fuels studied, in the temperature range from 200 to 300 K. This model should help in designing the new generation of fuels to meet the European standards and in preventing many of the problems associated with wax deposition during the handling of refined products.