Critical Causes of Cost Overruns in Marine Construction Projects: A PMBOK-Structured Assessment Triangulated with Documented Outcomes

Marine construction projects overrun their budgets more often and more severely than comparable onshore work, yet most prior studies rank candidate causes without connecting them to the final cost of real projects; this study closes that gap. A three-tier literature review followed by a three-round Delphi process produced 173 causes of cost overrun, organized under the eight performance domains of the PMBOK Guide (Seventh Edition). A paired probability–impact index elicited from 200 practitioners identified critical causes, a Monte Carlo simulation tested its stability, and perceptions were compared across stakeholder roles and experience bands with the Kruskal–Wallis test under a false-discovery-rate correction. The ranking was then compared with the documented results of 59 marine projects from Egypt and the Gulf, where the overruns averaged 18.7% and reached 60%. Escalation in resource prices, shortage of specialized materials, and contractor financial difficulty led the perception ranking, and the Delivery domain was the most influential of the eight. The documented record sharpened that picture: project attributes alone explained relatively little of the variation in overrun, whereas adding the breadth of documented causes substantially improved explanatory power. Resource-price escalation was the most common cause and a clear marker of larger overruns, while the worst cases were set apart by contractor-side failures and by delayed geotechnical and bathymetric surveys, a marine-specific planning failure that coincided with the highest overruns of any planning cause, although on eight projects only and with wide statistical uncertainty. Risk perception varied more with experience than with role. The findings direct attention toward contractor solvency screening and early subsurface investigation and provide a transferable model linking expressed concern to the domains where cost is actually lost.