| OneAdvent Limited |
| OneSavings Bank Plc |
| Onestream Limited |
| Only Natural Products Ltd |
| Open Social B.V. |
| Open Society Foundations (OSF) |
| Open University |
| OppenheimerFunds |
| Opportunity Bank |
| Options Consultancy Services |
| Oracle Corporation |
| Oracle Corporation UK Limited |
| Orange Organisation |
| Orange Tunisie SA |
| Orascom Construction Plc |
| Orascom Group |
| Org Beverages SARL |
| Organic Seed & Bean Co Ltd |
| Organisation for the Professional Empowerment of Women |
| Orient Productions |
| Orkla ASA |
| Ornua Co-operative Limited |
| Oromia Insurance S.C. |
| Orveon |
| Out of the Box |