Russia and Serbia signed on Saturday an intergovernmental agreement on deliveries of Russian natural gas to Serbia for the period until 2021.

The framework document envisions annual supplies of 5 billion cubic meters of natural gas by Russia’s energy giant Gazprom.

An addendum to the agreement stipulates that the future exports of Russian gas to Serbia will be carried out on condition that the Balkan country pays back $30 million for Russian gas supplied from November 2000 until January 2001 and about $10 million for supplies between 1995 and 2000.

The debt must be paid off in tranches by the end of 2014.

Russia is the main supplier of natural gas to Serbia. Gazprom delivered 1.4 billion cubic meters of gas to Serbia in 2011.

Under the current contract between Serbia’s state-run Srbijagas and YugoRosGaz, a Gazprom subsidiary in Serbia, the Balkan republic currently pays $470 per 1,000 cubic meters for Russian gas supplies.

Gazprom and Srbijagas will be signing contracts regulating the price and delivery volumes every year throughout the timeframe of the new agreement.