Oil storage tanks must be designed to withstand dynamic and seismic loads. It is very important to ensure the safety of oil tanks with large volumes under earthquakes. During the earthquake, the land surface moves in all directions and as a result, the tank is exposed to vibrations. Especially the movements parallel to the land surface create vibrations in the tank and cause unexpected deformations on the tank walls. In this study, possible deformations that may occur in oil tanks with three different geometries under seismic conditions are investigated depending on their filling ratios. In the study, a package program based on the finite element method was used. By observing the sample responses such as acceleration and deformation of the tested models, the results were compared and confirmed with previous studies. The results revealed a clear relationship between oil level, tank shape and mode change. The higher oil level offered higher natural frequency in any case. The response spectrum model observed an increase when the oil level increased.