If confirmed, it puts Cuba's [oil] reserves on par with those of the US and into the world's top 20. Drilling is expected to start next year by Cuba's state oil company Cubapetroleo, or Cupet.

"It would change their whole equation. The government would have more money and no longer be dependent on foreign oil," said Kirby Jones, founder of the Washington-based US-Cuba Trade Association. "It could join the club of oil exporting nations."

"We have more data. I'm almost certain that if they ask for all the data we have, (their estimate) is going to grow considerably," said Cupet's exploration manager, Rafael Tenreyro Perez.

Havana based its dramatically higher estimate mainly on comparisons with oil output from similar geological structures off the coasts of Mexico and the US. Cuba's undersea geology was "very similar" to Mexico's giant Cantarell oil field in the Bay of Campeche, said Tenreyro.