Royal Caribbean continues to expand its fleet with a new order for three additional cruise ships to be built during the next six years.

The paint is barely dried on Harmony of the Seas, the third Oasis-class ship, the largest and the fastest in the world, and only two weeks after its debut, Royal Caribbean announced its plans to build three more ships.

The US cruise giant has signed a memorandum of understanding with the French arm of South Korean shipbuilder STX to build three new vessels: a fifth Oasis-class ship and two other ships for its mysterious Project Edge class. The deal was signed only a few days ago and is worth 2.5 billion euros (US$2.8 billion), the shipyard said in an official announcement.

STX France is 66.6 per cent owned by STX Europe, which is a subsidiary of South Korea’s STX. 33.3 per cent are owned by the French state.

All three new ships will be built at Saint-Nazaire’s STX shipyard, where Royal Caribbean’s fourth Oasis-class ship and Celebrity’s other two Edge-class ships are currently being built. More details of what cruisers can expect onboard have not yet been released.

The fourth Oasis-class ship is expected to launch spring 2018. Like its sister Harmony of the Seas, it will carry 5,479 passengers, which is slightly more than Oasis and Allure. The ship will feature a mix of Oasis-class and Quantum-class amenities.

While the Oasis class ships are the largest in the world, Project Edge vessels keep their onboard touts “small-ship itineraries with large-ship amenities”, such as superlatively luxurious cabins, amenities, and culinary experiences.

The first two Edge Class ships are scheduled to debut 2018 and 2020, while the new wessels of the same class are slated for 2021 and 2022.