- Oficyna Wydawnicza Politechniki Wroclawskiej3
- OICC Press1
- Oil Gas Scientific Research Project Institute2
- Old City Publishing2
- OLES GONCHAR DNIPRO NATL UNIV2
- ONCOLOGY NURSING SOC1
- Oncology Nursing Society2
- Open Exploration Publishing Inc2
- ORTADOGU AD PRES & PUBL CO1
- OSA - The Optical Society2
- Osman Orhan2
- OVIDIUS UNIV PRESS3
- OXFORD UNIV PRESS11
- Oxford University Press13