- O Boticário
- OAS AG
- OFFIS Institute for Information Technology
- OMP France
- OMiLAB
- Oakland University
- Object Management Group
- Observatório do Valongo|UFRJ [Rio de Janeiro]
- Ocean College
- Oceaneering, Integrity Management & Digital Solutions
- Oceans and Atmosphere Flagship [Brisbane]
- Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office
- Ohio State University [Columbus]
- Ohio University
- Okan University
- Okayama University
- Old Dominion University [Norfolk]
- Onaos [Montpellier]
- Ontoprise GmbH [Karlsruhe]
- Open Government Data Austria
- Open University of the Netherlands [Heerlen]
- Oracle
- Orange Labs
- Orange Labs SOP|BIZZ|DIAM
- Orange Labs [Sophia Antipolis]
- Orkel AS
- Ortlinghaus-Werke GmbH
- Osaka Gakuin University
- Osaka Prefecture University
- Osaka University
- Osaka University [Osaka]
- Osaka University of Economics
- Osala Prefectuture University
- Oslo Metropolitan University
- Oslo and Akershus University College of Applied Sciences [Oslo]
- Ostwestfalen-Lippe University of Applied Sciences
- Otto-von-Guericke-Universität Magdeburg = Otto-von-Guericke University [Magdeburg]
- Oulu University of Applied Sciences
- Our Lady of the Lake University
- OvG University
- Oxfam GB
- Oxford Brookes University
- Oxford-Man Institute of Quantitative Finance
- Óbuda University [Budapest]
- Örebro University
- Özyeğin University
- Œuvre de village d’enfants