| 1 | OCR | Ocean Air PVT Ltd. | Callsign: Ocean Air, Ceased operations | MV | AVCODES |
| 2 | OCR | Oklahoma Central R.R. Co. | added 1/1988; eliminated 7/1990; 1/1994-7/2005 | | NAKINA |
| 3 | OCR | Oklahoma Central R.R. Co. | added 1/88; eliminated 7/90; 1/94-7/2000 | | NRHS |
| 4 | OCR | OKLAHOMA CENTRAL RAILROAD COMPANY | | | PWRC |
| 5 | OCR | Oklahoma Central Railroad | | | RSRV |
| 6 | OCR | OKLAHOMA CENTRAL RAILROAD CO | | | SCAC4 |
| 7 | OCRE | ORTEGA, CRESENCIO | | | SCAC4 |
| 8 | OCRI | OCEAN AIR TRANSPORTATION INC | | | SCAC4 |
| 9 | OCRM | Oak Capital Rail Management GmbH | | DE | VKM |
| 10 | OCRR | Ottawa Central Ry. | added 4/2000; 7/2000-7/2005 | | NAKINA |
| 11 | OCRR | Ottawa Central Ry. | added 4/2000; 7/2000 | | NRHS |
| 12 | OCRR | OTTAWA CENTRAL RAILWAY | | | PWRC |
| 13 | OCRR | Ottawa Central Railway | | | RSRV |
| 14 | OCRR | OTTAWA CENTRAL RAILWAY | | | SCAC4 |
| 15 | OCRR | Ottawa Central Ry. | | CDN | TRAFFIC |
| 16 | OCRS | OIL CARRIERS SHIPPING LIMITED | | | SCAC3 |
| 17 | OCRS | OCEAN RUN SEAFOOD CANADA LTD | | | SCAC4 |
| 18 | OCRV | OCOEE RIVER TRANSPORT INC | | | SCAC3 |
| 19 | OCRX | Oklahoma Central R.R. | 7/2000-7/2005 (not listed) | | NAKINA |
| 20 | OCRX | Oil Creek Refining Co. | 7/1923-7/1935 | | NAKINA |
| 21 | OCRX | Oklahoma Central R.R. | Jul-00 | | NRHS |
| 22 | OCRX | *OIL CREEK REFINING CO. | | | PWRC |
| 23 | OCRX | +OKLAHOMA CENTRAL RAILROAD | | | PWRC |
| 24 | OCRX | Oil Creek Refining | | | RSRV |
