A polydisperse molecular thermodynamic model is developed to predict the asphaltene precipitation in crude oil under reservoir conditions. Asphaltenes are characterized as a continuous family that follows a distribution function taken from the fractal aggregation theory. Discretization of the continuous family is made by using collocation points chosen as the roots of an orthogonal polynomial. It is assumed that the asphaltenes form a pseudo-liquid phase, free of other components. The parameters of the model were adjusted to fit experimental data available from the literature. A satisfactory representation of these data was obtained, showing a better agreement than the earlier models. A sensitivity analysis is performed in order to evaluate the influence of the model parameters on predicted values.