The nature and high sensitivity of complex products and development projects lead to increased complexity at operational and organizational levels requiring particular types of organizing & management styles. Identifying the key competencies required for project managers, especially those managing complex research and development (R&D) projects in the oil and gas industry, can increase the chance of project success. The main objective of this research is to identify the key competencies required for managing complex products and systems (CoPS) in R&D projects carried out in Iran's oil and gas industry. The Delphi-fuzzy approach is used to develop an effective measurement model based on group decision-making methods and fuzzy inference systems. The results and analyses of the model are used to determine the key competencies needed in the studied organization. The results demonstrate that risk management, system integration, and personal abilities with competency importance factors of 1.7, 1.6, and 1.6 respectively, are more important than other competencies while dealing with complexity in the projects studied.