The deal had been considered for some months and brings another vessel originally built for Renaissance Cruises' R series into the Oceania fleet.
In a note, analyst Tim Conder said Wells Fargo views the purchase as a 'strong commitment by NCLH to Oceania's successful niche of midsize destination-orientated cruises.'
Upon delivery in March 2016, Sirena will immediately undergo a 35-day, $40m refurbishment in Marseille to elevate the ship to the Oceania Cruises standard. It will gain specialty dining restaurants, Toscana and Polo Grill, along with more recent additions to the fleet such as Baristas and the cook-to-order grill at Terrace Café.
The ship will carry its first passengers in late April 2016.
'The acquisition of Sirena provides measured capacity growth based on the proven platform of Oceania Cruises' highly regarded mid-size ships,' said Norwegian Cruise Line Holdings president and ceo Kevin Sheehan.
The addition opens up new itinerary options, added Kunal Kamlani, president and chief operating officer of Oceania Cruises.
The inaugural season for Sirena will be released in late February, with reservations to open March 4.