The main objects of research were ground waters underlying the territories of oil terminals of the Baltic port. The areas most exposed to pollution during transshipment of oil and oil products were identified. As a result of monitoring studies it was found that groundwater pollution by soluble fractions of oil products is directly related to the spread of floating oil products layer. In addition, it was revealed that oil products in soluble form together with groundwater move much faster, polluting larger areas than in case of oil products layer spreading.