The Norwegian Cruise Line Holdings brand confirmed it will honour existing bookings made prior to 7 January which include passengers aged below 18.
However, all new reservations for future voyages will only be available to adult passengers.
The move means Oceana joins a handful of cruise brands to exclusively only welcome adults onboard along with Virgin Voyages and Ambassador Cruise Line.
Explaining the shift, Jason Montague, the line's chief luxury officer, said: "Our guests have consistently shared that the tranquil environment aboard our ships is one of the primary reasons they return time and time again.
“By transitioning to an adults-only experience, we are enhancing the very essence of the Oceania Cruises journey – one defined by sophistication, serenity and discovery.”
The line added that it carried out "extensive research which provided feedback from loyal repeat guests, experienced travel partners and new-to-brand guests".
"Feedback consistently showed that guests choose Oceania Cruises for its serene atmosphere, sophisticated service and unhurried pace, traits that are highly sought after and valued by mature, affluent travellers," it continued.
