Poor cost performance is a typical problem in construction projects where few projects were completed within the original estimated cost. The previous researches (literature) show that up to 90% of construction projects suffer cost overrun with amounts ranged from 5% to 200%. This paper first utilizes a literature review to identify cost overrun causes and categorizes such causes based on stakeholder, country, and project type. Secondly, an in depth review was conducted to identify the contractors' cost overrun root causes. Thirdly, contractors' gaps and shortage of cost management processes have been identified. Finally, guidelines were concluded to resolve the identified gaps and enhance cost performance. The research conclusions depict that the top five cost overrun causes were inflation and fluctuation of construction resources, inaccurate cost estimates, poor cost control, poor owners' financial status, and work scope change. In addition, this research manifests that two top contractors' related cost overrun factors, inaccurate cost estimate, and poor cost control, were deemed the main elements of the cost management system. Another major contribution of this research is addressing the gaps in cost management processes to pave the way for future studies on identified gaps