Before salvage work can begin to refloat or remove the Costa Concordia, there are 500,000 gallons (2,300 tons) of heavy fuel and 45,000 (200 tons) of diesel oil in the tanks of the stricken vessel which need to be extracted.
Dutch company Smit (based in Rotterdam), working with Italian firm Neri (based in Livorno), brought a barge alongside the ship as divers install external tanks that will collect the diesel.
Work to remove oil and fuel is expected to start soon and could take up to 28 days, depending on weather and sea conditions.
There are between 15-20 oil tanks that need draining. They are located against the outer wall which means salvage teams can attach a valve to the outside of the ship and drill in to reach the oil, without the oil escaping – a process known as hot-tapping.
As the Costa Concordia is no longer functioning for days, the heavy fuel got thick and viscous, making it harder to be pumped.
To remedy this, a steam-heated element is put through the pipeline to warm the oil, making pumping much faster.
The oil will be pumped to a barge and then to a larger offloading vessel.
Sucking out the oil creates a vacuum, so another hole is made lower down the tank to allow seawater to be pumped in, replacing the oil. This also ensures extracting the oil does not cause the vessel to shift position on the seabed.