In recent Decade, utilization of management and engineering indicators has become a common task. Among these indicators, Mean Time Between Failure (MTBF), Mean Time To Repair (MTTR) and Overall Equipment Effectiveness (OEE) are more popular. Iran Khodro as the largest car manufacturer company in Iran and in the Middle East to optimize its production lines, electricity has been substituted by compressed air power. To achieve this target, this company launched compressed air department that has 50 air compressors including centrifugal and screw types and this number was reached gradually through the years. In this paper, to investigate the status of the equipment and report to department managers OEE index has been used. Since this indicator is more commonly used for systems and equipment that has a specific production schedule, this paper by proposing new definitions and changes in OEE parameters, calculation of this index for one compressor has become possible. By having this index for each compressor, one can analyze the performance of each compressor alone or in comparison with the others and as a case study the OEE of ten compressors belonged to the compressed air department since march to august of 2017 have been calculated and analysis has been reported.