Madrid (CNN) -- An oil tanker captain was acquitted Wednesday of the central charge in what's widely considered Spain's worst environmental disaster -- a spill that blackened hundreds of miles of coastline.
Apostolos Mangouras, who was captain of the Prestige during the accident in 2002, was found not guilty of environmental crime.
He was, however, convicted on a lesser charge of disobeying orders from Spanish officials who tried to save the ship.
Mangouras was sentenced to nine months in jail. But Spanish legal experts said prison time is unlikely for someone sentenced to less than two years who has no prior criminal record.
If he had been convicted of environmental crime, he could have faced up to 12 years in prison.
Another Greek officer on the ship, Nikolaos Argyropoulos, was acquitted altogether. So was Jose Luis Lopez-Sors, former director general of Spain's Merchant Marine Department, the only Spanish government official charged in the case.
The three were not in court for the verdict.
The court ruled that a precise cause for the accident could not be established, so criminal responsibility could not be determined.
"No one knows with certainty what could be the cause of what happened, nor what should have been the appropriate response to the emergency situation created by the serious problem of the Prestige," the verdict reads. "But no one can deny the structural problem, nor could they show during the trial where that problem occurred exactly or why."
The group Nunca Mais, whose name means "never again," said it was studying the 263-page ruling. The group includes citizens and organizations that helped clean up the spill and served as a kind of class-action plaintiff in the case.
Pedro Trepat, attorney for Nunca Mais, called parts of the ruling "strange."
An appeal to Spain's Supreme Court is possible.
'Coast of Death'
The Prestige issued an alarm on November 13, 2002, during a storm with gale-force winds off northwest Spain in an area known as the Coast of Death, famous for numerous shipwrecks.
The ship reported it had a gash in its single hull and some of its cargo of 70,000 tons of fuel oil had started gushing out.
Spanish authorities soon ordered the stricken ship to move farther off the coast. It struggled for days but on November 19, at 8 in the morning and about 145 nautical miles off the coast, it split in two and sank.
Oil continued to leak from it, at the bottom of the Atlantic, in the ensuing days.
Much of this oil, described by some as having the sticky consistency of chewing gum, blackened hundreds of miles of coastline in Spain and neighboring France.
It was an ecological disaster, with dead and oil-laden birds as a painful reminder.
It was also an economic disaster for Spain's vital fishing industry, which was brought to a standstill for months over health concerns.
In 2003, the cost was estimated at about $5.7 billion.
But the court Wednesday did not assign damages to be paid because the defendants were acquitted of the principal charge of an environmental crime, which carried the potential for payments of damages, Trepat said.
CNN's Josh Levs contributed to this report.