The process of removing more than 2,300 tonnes of fuel from the strinken Costa Concordia has started.
Pumping began on Sunday afternoon, nearly a month after the ship ran aground on the island of Giglio.
Dutch salvage company Smit is conducting the operation to pump out the fuel, which is expected to take about four weeks to complete.
It will concentrate on the first of 15 tanks that are believed to hold around 84% of the fuel on board, the AP news agency quoted Italy’s civil protection department as saying.
Valves will be fixed to the tanks, allowing oil to be pumped through a hose on to a crane barge alongside the vessel. From there the oil will be transferred to a waiting oil tanker.
Meanwhile, Italian president Giorgio Napolitano and other senior officials attended a memorial mass in Rome on Sunday for the victims of the tragedy.
Napolitano said he was sorry that what transpired “was the responsibility of Italy and Italians”.
“We must continue to investigate,” he told reporters outside the basilica. “Prosecutors deserve respect for the job they’re doing.”
To date, 17 people have been certified dead from the disaster, while 15 remain unaccounted for.
The captain, Francesco Schettino, is under house arrest, accused of manslaughter, causing a shipwreck and abandoning the ship before all the passengers had been evacuated.