This paper presents the development and implementation of a computer program to assess and judge the operator performance both for control-room and field operators. In order to evaluate the performance of workers, several Operator Performance Indicators (OPIs) are defined and relevant human factors are carefully attributed. In this work, a number of operator skills based and depending on physics, emotion, technique, equipment, plant layout, process features, knowledge, conventional and abnormal operating conditions, time, weather, and environment are discussed. A mathematical model quantifies the OPIs and produces both qualitative judgments and quantitative marks characterized by an aseptic, unbiased and objective evaluation. The proposed methodology can be used not only for assessing the operators but also for scheduling training courses, future recruitments and deployment specifications.