Hellenic Petroleum has been named preferred bidder for a gas drilling block offshore western Greece, the country's largest refiner said on Dec. 6.

In a venture with Italy's Edison and Energean Oil, Greece's sole oil producer, Hellenic Petroleum, is searching for oil in three onshore and offshore blocks in western Greece.

"After the ratification of the lease agreement by Parliament, we are ready to immediately start exploration activities to discover the subsurface oil potential of the Kyparissiakos Gulf," Hellenic Petroleum CEO Grigoris Stergioulis said in a statement.

Athens tendered 20 offshore blocks in 2015 in the Ionian Sea and south of the island of Crete for deepsea oil and gas drilling, and unsealed the offers in February.

Greece has made several fruitless attempts over the last 50 years to find big oil and gas reserves. It has stepped up its efforts in recent years, prompted by a prolonged debt crisis and important finds in other countries.