O
- Observatorio medioambiental
- Occasional papers from the Osaka Museum of Natural History
- Ocean & coastal management
- Ocean dynamics
- Ocean science discussions
- Ocean science journal
- Ocean development and international Law
- Ocean dynamics
- Oceanología
- Oceanologica acta : revue européenne d'océanologie
- Oceanology / Industrial Research
- Oceans /Oceanic Society
- Oceanus : reports on research at the Woods Hole Oceanographic Institution
- Oceanus : the magazine that explores the oceans in deep
- Offshore : the journal of ocean business
- Ohio geology
- Ohio journal of science, The
- Open geology journal, The
- Open hidrology journal, The
- Open mineralogy journal, The
- Open paleontology journal, The
- Óptica pura y aplicada
- Options méditerranéennes. Série A: séminaires méditerranéens
- Ore geology reviews
- Organic and biomolecular chemistry
- Organic geochemistry
- Organisms diversity & evolution
- Origins of life and evolution of the biosphere
- Ozone: science & engineering