- Oasis (1973)
- Oasis of the Seas (2009)
- Ocean Adventurer (1975)
- Ocean Albatros (2023)
- Ocean Countess (1976)
- Ocean Diamond (1974)
- Ocean Dream (1981)
- Ocean Empress (1982)
- Ocean Explorer (2021)
- Ocean Jewel of St. Petersburg (1982)
- Ocean Life (1981)
- Ocean Majesty (1966)
- Ocean Monarch (1955)
- Ocean Nova (1992)
- Ocean Odyssey (1955)
- Ocean Odyssey (2022)
- Ocean Pearl (1967)
- Ocean Pearl (1970)
- Ocean Princess (1999)
- Ocean Princess (2000)
- Ocean Victory (2020)
- Ocean Village Two (1990)
- Oceana (2000)
- Oceanbreeze (1955)
- Oceanic (1965)
- Oceanic II (1966)
- Oceanic Grace (1989)
- Oceanic Odyssey (1989)
- Odessa Sky (1975)
- Odin (1972)
- Ola Esmeralda (1966)
- Old Club (1977)
- Olga Androvskaya (1977)
- Olga Sadovskaya (1977)
- Olympia (1953)
- Olympia Countess (1976)
- Olympia Explorer (2002)
- Olympia Voyager (2000)
- Olympic (1956)
- Olympic Countess (1976)
- Olympic Explorer (2002)
- Olympic Voyager (2000)
- Olvia (1976)
- Omar III (1972)
- Omar Star (1992)
- Opera (1980)
- Orange Melody (1980)
- Oriana (1995)
- Orient Explorer (1943)
- Orient Express (1975)
- Orient Queen (1968)
- Orient Queen (1989)
- Orient Queen II (1989)
- Orient venus (1990)
- Oriental Dracon (1972)
- Oriental Pearl (1967)
- Orion (1943)
- Orion (2003)
- Orion II (1943)
- Otto Sverdrup (2002)