While energy prices continue to climb, it conservation remains the prime concern for process industries. The daily growth of energy consumption throughout the world and the real necessity of providing it, shows that optimization of energy generation and consumption units is an economical and sometimes vital case. Hence, the optimization of a petroleum refinery is aimed towards great production and an increase in quality. In this research, the atmospheric distillation unit of the Iran-Arak-Shazand petroleum refinery was subject to optimization efforts. It was performed by the means of using a simulator with the aim to earn more overhead products. In the next step the optimization results from the simulators were carried out in the real world, at the above mentioned unit. Results demonstrate that the changes in the real operating conditions increase the overhead products with desirable quality. Finally, a net economical balance between the increments of the overhead products and the energy consumption shows an energy saving in this refinery.