Despite technological advancements and enhanced safety regulations by the International Maritime Organization, oil spill accidents continue to happen and pose a serious problem. For the prevention of these accidents, hence, it is of utmost importance to analyse them from different aspects exhaustively. Taking oil spill accidents falling into the International Oil Pollution Compensation Fund (IOPC Fund) scope into account, this paper attempts to investigate the influencing factors of spill accidents for tanker vessels comprehensively. For this goal, this paper utilizes the combination of the Classification and Regression Tree (CART) method and entropy- weighted Grey Relational Analysis (GRA) approach. The outcomes of this paper indicate that accident type and the flag of a vessel are the most influential variables that affect the size of oil spills. Shipowners, petrol importing companies and IOPC Fund officials can utilize the outcomes of this paper for mitigating oil spill risks stemming from tanker vessels.