A spill of 328 metric tons of heavy fuel oil happened in an Oil Terminal during the discharge of the product from a ship vessel to a storage tank. At 10.30 p.m. the discharge to storage tank No 375 was started by 2 operators. At the same time discharging to tank No 304 was ongoing. When reading the level indicator the operators noticed that the level in T375 didn’t continue to increase. They tried to increase the flow by reducing the valve to tank No 304. At 01.52 a.m. they discovered that the manhole of T375 was open and oil was flowing out to the ground outside the tank and to a neighbour company in the harbour. They closed the valve to T375 and the manhole and informed the terminal manager and a local cleaning company. At 03.00 a.m. the cleaning operation started. The harbour service staff inspected the harbour rain water drainage system and closed its outlet. Oil booms were placed in the open port harbour. Cleaning procedures continued during the following day. The authorities were informed about the accident. On 22/06, a Coast Guard noticed the first indication of the large environmental effects. Approximately 50 t of oil passed the rain water drainage system, reached the open sea and contaminated beaches and seashores.The spill resulted in a contaminated area in the harbour of approximately 2000 2500 m². Fishermen tools, hundreds of yachts and many birds were contaminated. The total economic loss was approximately 2,7 millions.The major factors which contributed to the accident were a lack of communication between the 2 shifts at the shift take over, absence detailed check lists for tank preparation and start-up process and of the equipment double-check before start-up, and the failure to respect operational procedures. Due to the Midsummer Eve holiday there were less personnel in the Oil Terminal than usual. The shift foreman was on vacation and the terminal manager had taken over the foreman’s work. The wide consequences of the accident were caused by the wrong reaction of the employees who assumed there was some problem with the incoming flow but did’nt go out and inspect the tank, the failure to respect the emergency plan which specify that the harbour should be informed immediately and the absence of bund and valves in the rain water drainage system. Moreover, the the water drainage systems and booms were less efficient because of density of the product (higher than 1). After this accident, the operational procedures, emergency response, organisational related areas, communication and design of the harbour were improved.