Royal Caribbean Cruises has signed a memorandum of understanding with French Shipbuilder STX France to build a fifth Oasis-class ship for delivery in the spring of 2021.

As part of the deal STX has also signed to build two additional Edge-class ships scheduled for delivery in the autumn of 2021 and 2022.

“The response to the arrival of Harmony of the Seas is staggering, eliciting excitement from eager cruisers from markets on both sides of the Atlantic,” said Richard Fain, chairman, Royal Caribbean Cruises.

“And Edge-class is one of the most highly anticipated new projects, following the high bar of Modern Luxury design set by its predecessor, the Solstice-class.”

The ships are for the Royal Caribbean and Celebrity Cruises brands respectively.

“The Oasis-class ships have delivered beyond expectations each time,” said Michael Bayley, president, Royal Caribbean International.

“Harmony of the Seas’ warm reception is evidence that growing this class of ship will continue to drive exceptional performance for the brand.”

This order is contingent upon the completion of customary conditions, including documentation and financing.

Final contracts, which include the definitive payment schedules, are expected to be completed within the quarter.

Capacity increases for 2016 through 2020 remain unchanged.