The high of oil demand as a fuel causes the demand for supply to the community is also high. Therefore, the intensity of Indonesia's tanker shipping vessel also increased. Ship accidents can cause oil spills. Polluted seas and loss of lives are the result of oil spills. To tackle shipwreck accidents that result in oil spills, IMO issues related rules to prevent damage, including the HNS Convention. The Convention requires restrictions on costs incurred by the ship owner to prevent damage to oil spills. But until now Indonesia has not ratified the regulation. The Formal Safety Assessment method is used to assist the steps in risk assessment and cost benefit analysis calculations if Indonesia considers ratifying the HNS Convention and its amendments. This method is used to identify potential hazards, determine the risk profile of each accident case and calculate the costs and benefits when ratifying the HNS Convention. The purpose of this research is to know the potential danger causing the oil tanker to have an oil spill accident, to analyze the cost of clean up given the happening of oil spill, and to recommend how far the ratification needed to regulate the compensation cost in case of tanker accident along with the effect obtained when considering ratifying the relevant rules. The result of this research is the potential of ship accident causing oil spills such as fire, sinking, aground and collision. The risk profiles of all types of ship accidents are at level 9, level 10 and level 11. The cost of clean up for oil spill accident cases is varied, with the smallest cost of US $ 1,950 and the largest cost of US $ 390,000. Based on the calculation of the cost and benefit shows that Indonesia needs to ratify the HNS Convention.

Keywords : HNS Convention, Formal Safety Assessment, Risk, Cost and Benefit.