HAVANA, Cuba (AFP) — Cuba is organising a new search for oil in the Gulf of Mexico after four earlier exploratory wells failed to make commercially viable finds, a state official said Monday.

The new round of drilling in Cuba’s exclusive economic zone in the Gulf of Mexico is set to begin in late 2016 or early 2017, said Osvaldo Lopez, head of offshore exploration at state oil company Cupet.

He told state television that Venezuela’s PDVSA and Angola’s Sonangol will drill for oil at depths of 1,500 meters (4,900 feet).

“We have evidence there are deeper areas generating that oil. What we’re trying to do is find a way to get to it,” he said.

International experts say the area probably holds five to nine billion barrels, while the government estimates there are as many as 15 billion barrels in untapped reserves.

Cuba’s exclusive economic zone in the Gulf of Mexico covers 112,000 square kilometers (43,250 square miles).

PDVSA, Spain’s Repsol, Russia’s Gazprom Neft and Malaysia’s PC Gulf have previously drilled offshore wells, but concluded they were not commercially viable.

Cuba produces about 25 million barrels of oil a year from wells on land and offshore, but that covers less than half the island’s consumption. The rest it imports from Venezuela on favourable terms of payment.

Cuban crude is for the most part extra-heavy and used only for electric power generation and the production of cement, lubricants and asphalt.

Last month, Cupet said it was open to negotiating exploration deals with US oil companies.