A Spanish court gave the sentence to Apostolos Mangouras of Greece for disobeying orders from authorities who attempted to save the tanker Prestige, but acquitted him of environmental crime for which he could have faced up to 12 years in prison, CNN reported.
Another ship officer, Argyropoulos Nikolaos, and Jose Luis Lopez-Sors, former director general of Spain's Merchant Marine Department, were acquitted of all the charges against them.
The ship's hull was gashed during a storm in November 2002 and some of its 70,000 tons of fuel oil gushed out, covering hundreds of miles of coastline.
Days later, the ship sank and oil continued to leak from the vessel as it sat at the bottom of the Atlantic.
The court ruled that a cause for the accident could not be determined so the defendants couldn't be blamed for the spill.
"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 read.