This paper presents one of the procedure to obtain stress distribution in transverse structural members of oil tanker in a design wave which is expected to produce the maximum water pressure corresponding to each probability level at bilge part. The fluctuating water pressure response at each part of the transverse ring to be studied is calculated by strip theory for 16 wave lengths and 7 heading angles (every 30 degree) at full loading condition, and the expected maximum fluctuating water pressure corresponding to each probability level is obtained using the ISSC wave spectrum and Walden's long term data of wave in the North Atlantic. The heading angle χ₀ and wave length λ₀ of the design wave are those which give maximum fluctuating water pressure response at selected part, and the wave height H _d is determined so as to produce the water pressure equivalent to the maximum value corresponding to each probability level. In the three dimensional transverse frame analysis, the internal cargo oil pressure is calculated considering the acceleration caused by the ship's motion. The sloshing effect is not included. In this paper we present stress analysis for the following conditions : (a) stress distribution in transverse ring at each probability level. (b) stress fluctuation during one wave period. (c) approximate long term distribution of fluctuating stress.