| Carrier Code | Carrier Name |
| ONGC | OIL NAVIGATION CORPORATION |
| ONGM | OCEAN & GULF MARITIME S A |
| OOLU | ORIENT OVERSEAS CONTAINER LINE LTD. |
| OPDU | OLDENBURG-PORTUGIESISCHE DAMPFSCHIFFS-RHEDEREI GMBH |
| OPFL | OPAL FINANCE LTD |
| OPTR | OPTI-TRANS INC |
| ORAD | ORADELL ENTERPRISES SA |
| ORCO | OHIO RIVER COMPANY, THE |
| ORSR | ORIENT SHIPPING ROTTERDAM B V |
| ORTR | ORION TRANSPORT LTD |
| ORTW | OSWEGO RIVER TOWING LINE INC |
| OSAI | ORINOCO SHIPPING AGENCIES INC |
| OSGC | OSG CAR CARRIERS INC |
| OSHC | ORCHESTRA SHIPPING COMPANY LIMITED |
| OSHI | OCEANSTAMINA SHIPPING LIMITED |
