Must be a Marriott Rewards member according to the T&Cs:

"1. Eligibility: The Marriott Rewards Moments Oceania Cruise Sweepstakes (the "Sweepstakes") is open to legal residents of the fifty (50) United States (including the District of Columbia), Canada (excluding Quebec), and the United Kingdom who, as of date of entry, are Marriott Rewards members and at least eighteen (18) years of age or the age of majority in their respective states/jurisdictions of permanent residence, whichever is greater. "