This paper investigates fuzzy troubleshooting of a complex crude oil desalination plant. First, probable plant faults and all the related information were investigated. Then, based on the collected data, proper membership functions and consistent rules were prepared. In the next step of study, the Mamdani fuzzy inference system was utilized. Finally, the proposed expert system was employed to recognize faulty performance of the plant. Comparing the proposed model with plant data, it was found that the proposed system is capable of fast and accurate trouble shooting of the plant. In addition to the trouble shooting, the system can also be used for operator training. (C) 2010 Elsevier B.V. All rights reserved.