Greece can help resolve Europe's energy insecurity with its untapped resources, Prime Minister Antonis Samaras said on Monday.
"There is the potential for very substantial sources in our area," Samaras told an international energy conference in Athens.
"Greece can play a key role to alleviate ... Europe's energy insecurity," he added.
The cash-strapped Greek state hopes for several billion euros (dollars) in revenue over the next 15 years from hydrocarbon caches which it believes lie in the Ionian Sea and near Crete.
The gulf of Patras is thought to hold some 200 million barrels of crude oil, while another 50-80 million barrels are believed to lie near Ioannina and another three million barrels near Katakolo.
Greece last year picked a Norwegian contractor to carry out seismic surveys in the Ionian Sea and south of Crete in search for oil and gas.
Drilling contracts for the region are to be issued in 2014.
Now that energy sources have been discovered within Cyprus and Israel's exclusive economic zones there is a high degree of certainty "that they also exist within Greece's exclusive economic zone in the southeast Mediterranean..." said Samaras.
"Soon Greece will play a major part in the production of European energy sources," he added.
Greece, Italy and Albania earlier this month signed an agreement to support the Trans Adriatic Pipeline (TAP) project designed to bring natural gas from the Caspian Sea to Europe.
The consortium developing the huge Shah Deniz gas field in Azerbaijan will decide by the end of June whether to pick TAP or rival pipeline Nabucco as its preferred transport route to Europe.
Meanwhile, Greece has to be mindful of a possible challenge in hydrocarbon exploration in the Aegean Sea by traditional rival Turkey.
Samaras on Monday said Athens had already advised the United Nations that Ankara had authorised exploration in areas south of Rhodes that Greece considers its own.
"We invoke the law of the sea, to which we are signatories," Samaras said.
"The other side invokes it without having signed it," the PM added.
"The best way to resolve differences is through respect for international law," said Samaras, who is due to visit Turkey in March.