Natural gas is one of the most common energy sources in modern society. In addition to economic, it has a strong strategic and political role in the modern world in which we live. Its price is largely impacted by the source from which it is supplied, the distance to the location of use as well as the possibility of supply from several different sources. Diversification of natural gas supply routes for each country or region is crucial for the security of supply by this energy source. The paper describes the state of the natural gas market, transmission capacities and needs, expected transmission from new supply routes, as well as the problems and risks the region is currently facing. The Ionian-Adriatic Pipeline (IAP), as a link to the Trans-Adriatic Pipeline (TAP) by which natural gas supply from remote production fields in Azerbaijan is planned, is a very important new (for some even the only) source of natural gas to Southeast European countries - Albania, Montenegro, Croatia and Bosnia and Herzegovina. It is also an additional diversified supply route and an alternative for Central European countries via the Croatian transmission system. The Ionian-Adriatic Pipeline is an essential strategic project which significantly increases the energy connection of Southeast Europe with the EU countries. This paper analyses several aspects of the construction of the IAP system - financial, environmental impact of the project, socio-economic environment of the project and project risks that accompany each investment. The potential of the project in terms of energy as an important factor of security of supply (sometimes the only one) in the region of Southeast Europe is presented. Moreover, the paper analyses the project objectives separately for each of the participating countries and as a unique technological unit. It also refers to the development of the existing transmission systems in the region, the existing availability of primary energy, as well as security of natural gas supply before and after the IAP system construction. Furthermore, the paper presents an analysis of investment costs – capital and operating investment in a period of 20 years of the system exploitation. In addition, positive financial effect of the project during the construction period are analysed. Finally, this paper identifies significant difference between the profitability of the parts of the IAP system due to different transported quantities and lengths of the gas pipelines that need to be constructed. Therefore, it is justified to observe the project as several units, that is, several separated projects with different business and development scenarios