Short-cut models of distillation are useful in screening design options for separation of petroleum fractions at conceptual design stage. A methodology for prediction of detailed product distribution for distillation processes using short-cut calculations of distillation is developed in this work. The proposed delumping procedure is explained in this paper, and an illustrative example is presented to elucidate the application in modeling of distillation using short-cut calculation methods. The proposed methodology helps retain molecular information of composition of petroleum fractions and may help extend the premise of molecular components-based modeling to separation processes such as distillation.