The Turkish strait is one of the most important routes of oil transportation. It connects the Black Sea and the Mediterranean, and it enables the transportation of oil produced in the north of Black Sea to Europe directly. The oil spill problem originating from tanker accidents is one of the major topics concerning the safe ship operation in Turkish straits. There have been large accidents occurring alongside a mega city, Istanbul, which has thirteen million inhabitants. A tanker accident in Istanbul strait can be a great disaster that directly affects life in the city. The present paper describes the numerical simulation of an oil spill in Istanbul strait enabling us to estimate the effect of an oil spill if a tanker accident occurs. Using the Star-CD code, a simulation was performed in the transient mode.