Belarus has said it asked Russia, the world's top crude producer, to supply its two refineries with 23 million tonnes of crude next year, while Russia is offering to deliver 18.5 million tonnes.
"There is no decision on next year's volumes, talks are still under way," said Transneft's spokesman, Igor Dyomin.
He said Russia would increase crude supplies to Belarus by 400,000 tonnes, compared with the previously envisaged volumes, to 5.025 million tonnes in January-March.
Clashes over energy pricing and pipeline transit with Belarus and Ukraine have over the past decade led to cuts or halts in Russian oil and gas supplies to central and western Europe.
These have most often happened over the New Year, when Russia has failed to agree on energy supply terms with the two countries.