Major shareholders Paneuropean Oil and Industrial Holding and the Greek government agreed last month to divest at least 50.1 percent of Hellenic, Europe's third largest oil refiner based on its market value of 2.4 billion euros (2.1 billion pounds).

The exact size of the stakes to be sold in an all-cash transaction will not be disclosed until short-listed investors are invited to submit binding offers.

The extension followed a request by interested investors, a source close to matter said.

(Reporting by Angeliki Koutantou; editing by Jason Neely)