This article analyses methodological issues which emerge in case someone attempts to make a comparative quantitative analysis of the overall maritime potential possessed by various countries. The author suggests possible solutions for those problems and also proposes a system, which can help to make an assessment of countries’ capabilities to have control of the sea, to exercise jurisdiction over the sea zones and to use the sea for a variety of their purposes. This system forms the index of maritime power of a nation, which is an overall quantitative expression of these capabilities. The overall index is based on four sub-indexes: maritime resources, maritime instruments, navy, maritime activities.