Some 14.3 million shares of the company traded in one block deal at a price of 0.3953 lei apiece, Bucharest Stock Exchange data indicated.
The parties to the deal were not disclosed.
In regular trading, blue chip OMV Petrom was up 0.76% at 0.396 lei by 1307 GMT on the Bucharest bourse.
(1 euro = 4.5189 Romanian lei)