Cost - benefit analysis is the process of evaluating of the cost and benefits of risk reduction measures. In this step,if the benefits of a risk reduction option have a higher value than the cost of measure values, it may be selected and applied. In the case of Bosphorus, for each accident factor when the risk is reduced by 20%, the numbers of accidents and danger level may be decreased substantially. If ships are monitored more carefully in terms of the prevention of ship based accidents, ship based risk may be reduced and at least 15 ship based accidents may not occur. Total risk may be reduced by 3.83% and for other accident types similar results may be seen