The optimization of chemical processes has gained immense importance in the present day. This work is aimed at the on-line optimization of an industrial crude distillation unit (CDU). A nonlinear, steady-state CDU model has been developed in-house for this purpose. Model tuning parameters in the form of vaporization efficiencies were incorporated to minimize the discrepancy between the measured and simulated column parameters on-line. The crude feed composition, represented by the true boiling point (TBP) curve, is known to vary with time. A procedure was developed to back-calculate the TBP curve using on-line plant data. Finally, the objective function was formulated to simultaneously maximize the net achievable profit and set the product properties within a user-specified range. The entire scheme was tested using real plant data off-line, but the problem formulation is suitable for supervisory-level on-line optimization without further modifications. It is shown that substantial increases in profitability can be achieved using supervisory on-line optimization.