Ensuring security of supply for the domestic natural gas market is one of the priorities of Serbian energy sector development. In the natural gas sector, the Republic of Serbia is strongly dependent on Russian gas. Import dependency is almost 80% and gas is imported via a single supply route. In order to evaluate the security of the natural gas supply in Serbia and vulnerability to possible interruptions in international supply chains, three possible scenarios for natural gas infrastructure development and two scenarios of natural gas consumption by 2025, are discussed in this paper. This combination of infrastructure and demand scenarios projects six possible futures for the Serbian natural gas system, assessed by N-1 index. This paper presents a methodology for determining maximal daily consumption for households and district heating (with a probability of once in 20 years) based on degree-days. The possibilities of the Serbian gas system mitigating the consequence of a possible supply cut from Ukraine, for six analysed scenarios are discussed.