The present publication of the “Southern Corridor Gas Regional Investment Plan” is the third edition of a report aimed at gathering and processing information from TSOs of countries which surround or are more directly influenced by the gas transportation route de- fined as “Southern Corridor”. As in the second edition, we tried to offer to the reader a complete picture of the Region mainly through the “Assessment and Market analysis” chapter, including the examination of congestion at Regional IPs, and “Network Assessments” chapter, where we show modelling results for the security of supply issue and the response of the gas flows to the gas supply price signals. Results reflect all the specific attributes of the area which the readers of this document have to take into account, in particular: \\ This Region hosts new transmission projects with larger capacities than planned infrastructure in the other Regions. Therefore new potential volumes will have high influence on security of supply and diversification of routes and/or sourc- es in the States of the area and all over Europe. \\ Many of the members of the Southern Corridor Region are transit countries, while infrastructure in other Regions has more a balanced role, being mostly destined to handle internal consumption. \\ This Region gathers countries with great variety of their national production. From one side, we have systems where production is from 0% to 10% of their peak consumption and may only marginally contribute to cover gas demand even in normal circumstances, let alone during crisis situation. On the other side, there are countries where production is a significant element in the supply mix, representing a substantial factor for the diversification of sources both for themselves and for their neighbours as well. Nevertheless the gas production volume in all producing countries of the Region follows a decreasing trend. \\ Such mixed picture can be seen also at the demand side, which is affected by different population sizes of member states, by their geographical spread, from central parts of Eastern Europe, with high consumption in winter periods, to Southern Europe countries, with relatively high consumption levels also during summer and finally, by different market maturity. Despite these differences all the countries, in the Region, and their TSOs, will be strongly affected by the construction of any of the big transmission projects and are prepared to adapt their investments to such possibilities.