For the second time this year, exploratory drilling in Cuban waters of the Gulf of Mexico has failed to find oil and gas in commercially viable quantities, state-owned Cubapetroleo said Monday.

The "active petroleum system" detected by Malaysia's PC Gulf and Russian firm Gazpromneft does not constitute a "commercial discovery," Cubapetroleo said in a statement published in the communist-ruled island's official media.

The effort was conducted at a depth of 4,666 meters (15,298 feet) in waters off the coast of the western province of Pinar del Rio, using the Scarabeo-9 rig.

An earlier foray with the same rig by Spanish oil company Repsol also produced disappointing results.

PC Gulf and Gazpromneft are not giving up, Cubapetroleo said, and plan to carry out three-dimensional seismic analysis of other blocks in the coming months.

For now, Venezuelan state oil giant PDVSA is to begin drilling with the Scarabeo-9 rig at a spot off the Cape of San Antonio, Cuba's westernmost point.

Cubapetroleo says the island's Exclusive Economic Zone, a 112,000-square-kilometer (43,240-square-mile) area in the southeastern Gulf of Mexico, has "high potential for the discovery of new hydrocarbon reserves based on geological studies."

The EEZ comprises 59 blocks of approximately 2,000 sq. kilometers (772 sq. miles) each, 22 of which have been awarded to foreign oil companies.

Havana says the zone could hold as much as 20 billion barrels of crude, while other estimates put the EEZ's reserves at between 5-9 billion barrels.

Cuban oil production has remained unchanged at some 4 million tons annually for the past five years.

Global oil power Venezuela, cash-strapped Cuba's main ally, provides the Communist-ruled island with an additional supply of more than 100,000 barrels per day of subsidized crude and derivatives in exchange for services, mainly in the healthcare, education and sports sectors. EFE