World's Biggest And Expensive Ship - The Oasis of the Seas is the first of the Oasis Class (formerly the Genesis Class or project Genesis) luxury cruise ships in the Royal Caribbean International fleet. The 16-deck ship, which has an estimated build cost of $1.24bn, is the largest cruise ship afloat with a tonnage of 220,000gt (43% more than the Freedom Class ships) and a double occupancy capacity of 5,400 passengers in 2,700 state rooms.