Taking on fuel. The fuel consumption of the main engines at full power is 1,377 US gallons
(4338 UK gal) of fuel oil per engine per hour for the 16-cylinder engines and 1,033 US
gallons (860 imp gal) per engine per hour for the 12-cylinder engines.

Just as with large cars, larger cruise ships tend to have lower fuel efficiency, at least in gross terms.
To give the reader an idea of the fuel efficiency of large cruise ships, I'd like to use the
world's largest cruise liner as an example.

The MS Oasis of the Seas, completed in 2010, has a total length of 361.8 meters, a height of 72
meters above the sea line, and room in its 16 passenger decks for 6,296 passengers. At its
cruising speed of 22.6 knots (26 mph), the Oasis of the Seas burns 11361 gallons of fuel each
hour. The fuel efficiency, then, is 0.0023 mpg, or 12.08 feet per gallon!

I understand the Oasis can carry around 56,000 barrels of fuel oil. 42 US gals per barrel.