| Orealys | Haute-Garonne |
| Orega Biotech | |
| Oregon Therapeutics | |
| Orens | |
| Orentis | Paris |
| Oresys | Paris |
| Oresys | |
| Organicweb | Vaucluse |
| Organisation for Economic Co-operation and Development | |
| Organisation Systèmes d'Information Conseil | Bouches-du-Rhône |
| Oriade | Alpes-Maritimes |
| Oriale Informatique | Maine-et-Loire |
| Origame | |
| Orinoko | |
| Oriolis | Métropole de Lyon |
| Orion | Bouches-du-Rhône |
| Orius | |
| ORKE | |
| Orkis Ajaris | Bouches-du-Rhône |
| Orolia | Essonne |
| Orone Data Services | Paris |
| Orphalan S.A. | |
| Orson.io | Paris |
| Oryanoo | Val-de-Marne |
| Oscar Référencement | |
| Ose Immunotherapeutics | |
| Osimatic S.A.S. | Yvelines |
| OSInet | Essonne |
| Osium AI | |
| Osivax | |
| OSO-AI | |
| OSS Ventures | |
| Ostendi | Hauts-de-Seine |
| OT4B S.A.S. | |
| Otaree | |
| Otidea | Hautes-Pyrénées |
| Otium Capital | |
| Otovo | |
| OTSTC - Creative BIometric | Paris |
| Ouebsson | Loire-Atlantique |
| Ouest Communications Mobiles | Vienne |
| Ouest France - Start-up | Ille-et-Vilaine |
| Ouest-PC | Ille-et-Vilaine |
| OuestWare | |
| Ouidou | |
| Ouishare | Seine-Saint-Denis |
| Ouroboros Telecom | |
| Ourouk | Paris |
| Outiref | Bas-Rhin |
| Outmind | |