Affiliations with the Letter O
- Oak Ridge National Laboratory -- United States
- Oakbank Consultants -- Australia
- Occidental Chemical Corp. -- United States
- Ocean University of Qingdao -- China
- Odense University Hospital -- Denmark
- Office of Minister of Chemicals and Fertilizers -- India
- Ohio State University -- United States
- Okayama University -- Japan
- Oklahoma State University -- United States
- Örebro Universitet -- Sweden
- Oregon State University -- United States
- Organic Intermediates and Dyes Institute -- Russia
- Orta Dogu Teknik Üniversitesi -- Turkey
- Osaka City University -- Japan
- Osaka Prefecture University -- Japan
- Osaka University -- Japan
- Österreichische Akademie der Wissenschaften -- Austria
- Our Lady's Hospital for Sick Children -- Ireland