O
| Railway name | Locale | Operating years | Comments |
|---|---|---|---|
| Ontario and Quebec Railway | Acquired by CPR. | ||
| Ontario L'Orignal Railway | eastern Ontario | 1996–2001 | Acquired by OCR. |
| Orford Mountain Railway | Acquired by CPR. | ||
| Oshawa Railway | Acquired by CNR. | ||
| Ottawa and New York Railway | Eastern Ontario | 1898–1957 | Subsidiary of NYC. |
| Ottawa, Arnprior and Parry Sound Railway | Acquired by CAR. | ||
| Ottawa Northern and Western Railway | Acquired by CPR. |
Read more about this topic: List Of Defunct Canadian Railways