The uniqueness of megaprojects requires any effort to make sense of their behavior to successfully utilize expert knowledge. Success of industrial megaprojects relies heavily on the knowledge and experience of the owners, project managers, engineers, financiers and other organizations and parties within the project. This valuable project knowledge is held within organizations either as explicit and in documents, or, tacit and by the members of the project team. Quantifying and elicitation of this knowledge requires a framework that outlines its utilization. This paper outlines a methodology to systematically collect expert knowledge for probabilistic reasoning on megaproject behavior. The reasoning process is developed based on the failure path and driver view of project risk and failures mechanism. Results of a pilot survey study on the method, along with the created probabilistic model is presented.