The ruling opens the door to damage claims against the captain and the insurer, The London Steamship Owners Mutual Insurance Association, with one prosecutor calling for more than EUR4bn.
More than 13 years after oil spill, Mangouras, now 81, was on 26 January convicted of recklessness resulting in catastrophic environmental damage, according to a statement by the court, overturning a previous sentence which cleared him of criminal responsibility.
The Supreme Court ruling confirmed the acquittal of the Prestige chief engineer and of Jose Luis Lopez Sors, Spain’s former director-general of the Merchant Marine, but it slapped the tanker's owner Mare Shipping, and the International Oil Pollution Compensation Funds (IOPC) with direct civil liability.
The sinking of the 1976-built 81,000dwt Greek tanker, which was sailing to Gibraltar, released an estimated 63,000 tonnes of oil along the Galicia coast and forced the closure of the country’s richest fishing grounds.
The Galician regional court had previously concluded it was impossible to establish criminal responsibility and the spill was partly due to the 26-year-old tanker’s poor state of repair.
After a storm damaged one of its fuel tanks, the ship had spent days drifting at sea having been refused permission to dock by Spanish, Portuguese and French authorities. It eventually split into two and sank about 250 miles off the coast, spurting oil into the water from the sea bed.
Mangouras was accused of guiding the tanker in treacherous conditions with full knowledge of its weakened structure while the ship was overloaded by at least 2,000 tonnes of fuel oil.
The Supreme Court ruling overturned a 2013 decision of a lower court that acquitted him of most charges but sentenced him to nine months for disobeying authorities.
It is not known if Captain Mangouras, who spent 83
days in a Spanish jail after the incident will now actually serve jail time.
He lost a case against Spain in 2009 at the European Court of Human Rights when a Strasbourg court ruled his EUR3m bail and 83 days in jail did not violate the European Convention on Human Rights.
In the US the Spanish state sued the ABS, the Prestige's classification society. This ended in 2014 with a New York appeal court ruling the classification society could not be held liable for the casualty.