Mrakic said the deal would most likely be signed on Wednesday.
A preliminary agreement signed in Moscow on January 25 includes the acquisition by Gazprom's oil arm Gazprom Neft of a 51% stake in state-owned Naftna Industrija Srbije (NIS) for $400 million, Gazprom's $500 million investment in a gas storage facility in Serbia, and the construction of the Serbian segment of the South Stream pipeline.
Under the South Stream project, a 400-km (248-mile) leg will be built in Serbia for Russian natural gas supplies to and via the Balkans.
NIS produces around 1 million metric tons (7.3 million barrels) of crude annually, refines 7 million metric tons (51 million barrels) and has Serbia's largest network of filling stations.
Gazprom Neft, known as Sibneft before it was taken over by Gazprom in September 2005, produced 32.7 million metric tons (240 million barrels) of crude and posted a U.S. GAAP net income of $4.14 billion in 2007
