In this report, it is described the evaluation method of optimal cross section of breasting dolphins of deepwater terminals for crude oil tanker in oil manufacture factory. The cross section of the breasting dolpins are designed with single pile structures (SPS) for five values of ship's berthing force. And the failure probabilities of the breasting dolphins are computed for each cross section taking into account the randomness of ship berthing force in life time of structures. Also alternatives of transportations of crude oil and oil products in the case of failure of the dolphins are
presented. The evaluation formula is presented both increased cost and negative benefit for three alternatives in the case of the failure. And the ratio of cost
to evaluate the cost and negative benefit are investigated. Then, the optimal cross section is obtained based on the minimum total cost consept.