A thermodynamic framework is developed for calculating wax precipitation in multicomponent (nonferromagnetic) hydrocarbon mixtures under the influence of a static magnetic field. A mathematical expression was derived for calculating the compositional derivatives of the magnetic susceptibilities using an equation of state. These susceptibilities are required for calculating magneto-chemical fugacities. The model was used to predict the effect of a static magnetic field on crystallization temperature and amount of precipitated wax for three normal-paraffin mixtures and one synthetic gas-condensate. Calculated results indicate that static magnetic fields increase the probability of formation of paraffin crystals, in accordance to the experimental evidence. (c) 2006 American Institute of Chemical Engineers.