The refinery, which is majority-owned by Russia's Rosneft (ROSN.MM), has been a problem for the German government ever since Berlin ended its energy ties with Moscow last year.
As a result, Germany put Rosneft's 54.17% stake under trusteeship, essentially giving the government control over the asset while technically leaving ownership in the Russian group's hands.
That led Shell to revive plans to sell its stake in Germany's fourth-largest refinery, which supplies 90% of Berlin's fuel, earlier this year.
"Unimot is one of the possible buyers of the Shell share, but not the only one," a government source told Reuters.
Unimot last year said it was expanding international trading as it sought to import diesel to Germany amid European Union sanctions on Russian oil and refined products.
Germany is also no longer considering Kazakhstan's KazMunayGas (KMGZ.KZ) and its subsidiary Kaztransoil (KZTO.KZ) as possible buyers of the stake as they cannot guarantee the necessary stability for Schwedt, the source added.
Shell, Unimot and Germany's Economy Ministry, which is responsible for the trusteeship of Rosneft's stake in Schwedt, all declined to comment. Rosneft Germany did not immediately reply to a request for comment.
