Many researches have been carried out on the sloshing forces of liquid in a ship tank. But most of the researches have focused on the magnitude of the pressure at model tests, and there remain some problems regarding the method to estimate from the results of model tests the sloshing load acting on an actual ship tank. The authors present the results of investigation which they carried out in this respect taking into account the scattering of the data, and also the results of their study on the law of similarity. In this report, as a short term distribution of a sloshing load, a new probability function is offered, which is deribed on the assumption that the sloshing data at regular oscillation will scatter in a form of Rayleigh distribution. Next, how to extrapolate the experimental data to the load acting on an actual ship tank, including the case of gas entrapment at the time of impact, is discussed. And the characteristics of the sloshing load with gas entrapment is qualitatively investigated.