The article discusses the modern methods of determining the mode of low-frequency oscillations in a port causing harbor oscillations, using as an example the dry cargo area of the Taman seaport and the Gelendzhik seaport that are currently under design. These ports were scanned for risk of harbor oscillation occurrence through an existing regulatory procedure which uses significant simplifications. In order to obtain the resonance characteristics of the port areas, low-frequency wave processes in the port were calculated using the SWASH spectral model. As a result, the resonance properties of various port areas important for port design have been obtained. In this case, white noise was modeled at port entrance, and the gains of the spectral components at critical frequencies were found. It has been shown that the suggested approach allows to obtain the resonance frequencies of the designed harbor. Further development of this approach may result in obtaining the resonance energies as well.