The news was reported on Thursday by the Serbian TV channel B92, citing government sources.
Serbian economics minister Mladjan Dinkic is known to be a harsh critic of the deal's financial terms, saying they are too beneficial for Gazprom Neft.
A Serbian delegation led by President Boris Tadic will arrive in Moscow next week to sign three oil and gas deals with Russian energy giant Gazprom, a Russian diplomatic source said earlier on Thursday.
A preliminary agreement was signed in Moscow on January 25 on the acquisition by Gazprom's oil arm Gazprom Neft of a 51% stake in state-owned Naftna Industrija Srbije (NIS), plus Gazprom's $500 million investment in a gas storage facility in Serbia, and the construction of the Serbian segment of the South Stream pipeline.
On December 5, during talks with Gazprom CEO Alexei Miller in Belgrade, the Serbian president confirmed the agreements would be signed by the end of the year.
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 US GAAP net income of $4.14 billion in 2007.
