Delay is one of the most common causes of construction projects failure in Iran. The larger sizes of the projects, the more risks and costs of delays. In this paper, the causes of delays in EPC contracts of nonindustrial buildings were excavated from the related previous research and several interviews with experts of this subject, and adjusted by the brainstorming technique, Delphi and reconciling the nature of these projects. Then, a questionnaire was distributed among 52 experts working in the South Pars project, and the data were analyzed by descriptive and factor analysis methods. Descriptive analysis revealed that “Inflation and escalation of material prices and human resources salaries”, “Unrealistic contract duration and requirements imposed” and “Political situation” were the most significant delay factors. Meanwhile, factor analysis indicates that “Improper construction methods”, “Shortage of experienced and skilled labor” and “Long acceptance process (shop drawings, permits, tests and samples)” were the most important causes of delay.