In this paper the As-Is model of the organizational affairs process of the NIORDC (National Iranian Oil Refining and Distribution Company) was drawn by the use of BPMN modeling tool, and then its simulation model was modeled by using SIMPROCESS simulation software and relative parameters were defined. Necessary scheduling in defining simulation parameters were extracted and set according to available organizational documents and archives. Afterwards, justification and verification of simulation models were tested by using statistical tests. In the next stage, several reengineering scenarios were suggested and designed according to BPR rules, experts' viewpoints, brainstorming sessions, and the facts found during project implementation. These scenarios were modeled by using BPMN modeling tool, and then their simulation models were designed. Since these scenarios are about the future situation of the process, only some justification and verification steps of simulation models were considered. Finally, on the basis of defined indicators in the beginning of the project, values of them were calculated for each scenario and each one was analyzed on the basis of cost-benefit analysis. At last, these scenarios were ranked by using AHP method and their scores were counted in order to suggest to the management.