The statistical predictions of horizontal wave bending moment have been made for a gigantic oil tanker of 310 meters length and the similar ships of different lengths, in order to find out the long-term trends of horizontal wave bending moment and to examine the design values of those. Firstly, the response functions of horizontal wave bending moment are calculated by the aid of the modified strip theory. Then, the standard deviations of horizontal wave bending moment are evaluated based upon the linear superposition theory, by using the calculated response functions and the formulated wave spectra for given sea conditions. Finally, the long-term predictions of horizontal wave bending moment are determined by the obtained standard deviations and the wave statistics of the North Atlantic Ocean. According to the systematic prediction analysis, the longitudinal distributions of horizontal wave bending moment predicted with the exceeding probability of 10^-8 are investigated in relation to the ship speed, heading angle and ship length.