Glossary of maritime terminology
- OBO Ship
- OCIMF SIRE
- Officer
- Offshore Barge
- Offshore Construction Vessels
- Offshore Production Vessels
- Offshore Support Vessels
- Offshore Vessels
- Oil Exploration & Drilling Vessels
- Oil Purifier
- Oil Record Book
- Oil Tanker
- Oiler
- Oily Water Separator
- Online Maritime Directory
- Open Registry
- Ordinary Seaman
- Ore Carrier
- Ore-Oil Carrier
- Oscar
- OSV
- Outfall Buoy
- Overtonnaging