EU member Bulgaria has been criticised for its almost total dependence on Russia for its annual consumption of about three billion cubic metres of gas. It receives the gas via Ukraine - a route that Russian giant Gazprom plans to abandon in 2020 when its TurkStream project through Turkey becomes operational.
In a bid to secure alternative deliveries, the Balkan country had long planned to link its gas network to those of its neighbours - Greece, Serbia and Romania - but the projects were severely delayed by administrative hurdles.
The new 182-kilometre (113-mile) IGB pipeline between the Bulgarian town of Dimitrovgrad and the Greek town of Komitini is scheduled to open late next year.
It will allow Bulgaria to receive Caspian Sea gas from Azerbaijan's Shah Deniz field as well as LNG from various sources via terminals in Greece.
The project will cost 220 million euros ($245 million) and will have an initial annual capacity of three billion cubic metres of gas, which could be increased to five billion.