OBO

 Oil/Bulk/Ore

O/C

 Open Charter

 Ore Carrier

OCIMF

 Oil Companies International Marine Forum

OCP

 Over Common Point

OD

 Outside Diameter

ODME

 Oil Discharge Monitoring Equipment

ODP

 Offshore Drilling Platform

OH

 Off Hire

OHBC

 Open Hatch Bulk Carrier

OO

 Oil/Ore

 Owner's Option

OOG

 Out Of Gauge

OPA

 Oil Pollution Act

OPEC

 Organisation of Petroleum Exporting Countries

OPL

 Off Port Limits

OPRHNS

 Protocol on Preparedness, Response and Co-operation to Pollution incidents by Hazardous and Noxious Substances

OR

 Owner's Risk

ORB

 Owner's Risk of Breakage

ORC

 Owner's Risk of Chafing

ORD

 Owner's Risk of Damage

OS

 Ordinary Seaman

OSB

 One Safe Berth

OS&D

 Over, Short and Damage (report)

OSD

 Open Shelter Decker

 Oil Spill Dispersant

OSP

 One Safe Port

OSRA

 Ocean Shipping Reform Act

OSV

 Offshore Supply Vessel

OT

 On Truck

 Overtime

 Oil Tight

OWS

 Oily Water Separator