| OfiNET | Madrid |
| Ofitec Tècnica, S.L. | Tarragona |
| Ofiware | Madrid |
| OKA Servicios Internet, S.L. | Madrid |
| OKB Interactive Studio | Madrid |
| OKIODATA Ibérica Software | Valencia |
| Okirine Bio | Barcelona |
| okITup, S.L. | Girona |
| Olinet, S.L. | Málaga |
| Oliplus Servicios, S.L. | Valencia |
| Olivos by Design | Málaga |
| Omega 2001 Servicios Informaticos, S.L. | Madrid |
| Omitsis | Barcelona |
| Ommatidia LiDAR, S.L. | Madrid |
| Omnigaea, S.L. | Barcelona |
| Omnitel Comunicaciones | Madrid |
| On Services Sistemas y Servicios Informaticos, S.L. | Madrid |
| Ona Therapeutics | Barcelona |
| onBRANDING, S.L. | |
| Oncomatryx Biopharma, S.L. | Biscay |
| Oncostellae | A Coruña |
| Oncovision | Valencia |
| Ondata International | Madrid |
| Ondho | Barcelona |
| ONE digital consulting | Madrid |
| OneChain Immunotherapeutics | Barcelona |
| OneCoWork | Barcelona |
| Onenpro S. Coop. | Gipuzkoa |
| Online Marketing Group | Madrid |
| OnRetrieval | Madrid |
| Ontech | Sevilla |
| Ontic Soluciones, S.L. | Albacete |
| Ontinet.com | Valencia |
| Ontrace Intelligent Video Analytics | |
| Onum | |
| Onurabat, S.L. | Biscay |
| Onversed Technologies, S.L. | Málaga |
| Opcionalia Soluciones Avanzadas | Granada |
| Open Bank, S.A. | Madrid |
| Open Canarias | Santa Cruz de Tenerife |
| Open Cloud Factory | Biscay |
| Open Document Management System, S.L. | Balearic Islands |
| Open Future | Madrid |
| Open Xarxes Coop. V. | Valencia |
| Open2b Software S.n.c. | Pontevedra |
| OpenBootcamp, S.L. | Valencia |
| Openbravo, S.L.U. | Navarre |
| OPENETICS International, S.A. | Barcelona |
| Openfinance | Valencia |
| OpenHost, S.L. | Ourense |