| Name | Shipbuilder | Build Location |
|---|---|---|
| Barque Oleander | Unknown | Unknown |
| Ole Noller | Unknown | Unknown |
| Oliver Lang | Unknown | Deptford |
| Olizata | Unknown | Unknown |
| Olyian | Unknown | Unknown |
| Omeo | Unknown | Unknown |
| Omrah | Unknown | Unknown |
| Oona | Unknown | Unknown |
| Ophelia (1863) | John Reid & Co. | Glasgow |
| RMS Ophir (1891) | Robert Napier and Sons | Glasgow |
| Orama | Unknown | Unknown |
| Oregon | Unknown | Unknown |
| RMS Orient (1879) | John Elders & Co. | Glasgow |
| Origaba | Unknown | Unknown |
| Orirabu | Unknown | Unknown |
| SS Orizaba | Unknown | Unknown |
| Ormuz | Unknown | Unknown |
| Orontes | Unknown | Unknown |
| Orontes | Unknown | Unknown |
| Orotara | Unknown | Unknown |
| RMS Oroya (1886) | Barrow Shipbuilding Company | Barrow |
| SS Orsova (1909) | J. Brown Co. Ltd. | Clydebank |
| HMS Ortona | Unknown | Unknown |
| Oruba | Unknown | Unknown |
| SS Orvieto (1909) | Workman, Clark & Co.Ltd. | Belfast |
| Oscar Oidae | Unknown | Unknown |
| Oseth | Unknown | Unknown |
| RMS Oskerley | Unknown | Unknown |
| SS Osterley (1909) | London and Glasgow Shipbuilding Company | Clydebank, Scotland |
| Oswestry Grange | Unknown | Unknown |
| Otranto | Unknown | Unknown |
| Otto | Unknown | Unknown |
| Otway | Unknown | Unknown |
| Oujaba | Unknown | Unknown |
| Oval | Unknown | Unknown |
| Pacifique | Unknown | Unknown |
| Pahlant | Unknown | Unknown |
| Palmeira | Unknown | Unknown |
| Papa | Unknown | Unknown |
| Paparoa | Unknown | Unknown |
| SS Parmstadt | Unknown | Unknown |
| Partell | Unknown | Unknown |
| SS Paten | Unknown | Unknown |
| Pauline | Unknown | Unknown |
| Penthelselia | Unknown | Unknown |
| Pentho hire | Unknown | Unknown |
| Pentus | Unknown | Unknown |
| Pera | Unknown | Unknown |
| Percy | Unknown | Unknown |
| Pericles | Unknown | Unknown |