| 1 | Obesity Medicine 🔗 | 2016- | Clinical Key | 18 |
| 2 | Obesity Research & Clinical Practice 🔗 | 2007- | Clinical Key | 20 |
| 3 | Obstetric Anesthesia Digest 🔗 | 2001- | Ovid | 24 |
| 4 | Obstetrical and Gynecological Survey 🔗 | 1995- | Ovid | 23 |
| 5 | Obstetrics and Gynecology 🔗 | 1995- | Ovid | 17 |
| 6 | Obstetrics and Gynecology Clinics 🔗 | 2007- | Clinical Key | 22 |
| 7 | Obstetrics, Gynaecology and Reproductive Medicine 🔗 | 2007- | Clinical Key | 19 |
| 8 | Occupational and Environmental Medicine 🔗 | 1944- | BMJ | 19 |
| 9 | Occupational Medicine 🔗 | 1996- | Oxford | 25 |
| 10 | Ocular Immunology and Inflammation 🔗 | 1997- | Taylor & Francis | 25 |
| 11 | Ocular Oncology and Pathology 🔗 | 2015- | Karger | 22 |
| 12 | Ocular Surface 🔗 | 2007- | Clinical Key | 28 |
| 13 | Oncologist, The 🔗 | 2000- | Oxford | 19 |
| 14 | Oncology Research and Treatment 🔗 | 1998- | Karger | 22 |
| 15 | Oncology Times 🔗 | 2001- | Ovid | 25 |
| 16 | Open Forum Infectious Diseases 🔗 | 2014- | Oxford | 21 |
| 17 | Open Heart 🔗 | 2014- | BMJ | 22 |
| 18 | Operative Neurosurgery 🔗 | 2005- | Oxford | 18 |
| 19 | Operative Techniques in Orthopaedics 🔗 | 2007- | Clinical Key | 20 |
| 20 | Operative Techniques in Otolaryngology - Head and Neck Surgery 🔗 | 2007- | Clinical Key | 21 |
| 21 | Operative Techniques in Sports Medicine 🔗 | 2007- | Clinical Key | 19 |
| 22 | Operative Techniques in Thoracic and Cardiovascular Surgery: A Comparative Atlas 🔗 | 2007- | Clinical Key | 20 |
| 23 | Ophthalmic Plastic & Reconstructive Surgery 🔗 | 2000- | Ovid | 19 |
| 24 | Ophthalmologica 🔗 | 1998- | Karger | 22 |
| 25 | Ophthalmology 🔗 | 2007- | Clinical Key | 28 |
| 26 | Ophthalmology Science 🔗 | 2021- | Clinical Key | 24 |
| 27 | Optometry & Vision Science 🔗 | 2000- | Ovid | 19 |
| 28 | OR Nurse 🔗 | 2007- | Ovid | 45 |
| 29 | Oral and Maxillofacial Surgery 🔗 | 2007- | Clinical Key | 20 |
| 30 | Oral and Maxillofacial Surgery Cases 🔗 | 2015- | Clinical Key | 23 |
| 31 | Oral Oncology 🔗 | 2007- | Clinical Key | 22 |
| 32 | Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology 🔗 | (2012-2015) | Clinical Key | 18 |
| 33 | Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontology 🔗 | (2007-2011) | Clinical Key | 21 |
| 34 | ORL Journal for Oto-Rhino-Laryngology, Head and Neck Surgery 🔗 | 1998- | Karger | 19 |
| 35 | Orthopaedic Nursing 🔗 | 2001- | Ovid | 22 |
| 36 | Orthopaedics & Trauma 🔗 | 2009- | Clinical Key | 20 |
| 37 | Orthopaedics & Traumatology: Surgery & Research 🔗 | 2010- | Clinical Key | 18 |
| 38 | Orthopedic Clinics of North America 🔗 | 2007- | Clinical Key | 20 |
| 39 | Orthoplastic Surgery 🔗 | 2020- | Clinical Key | 19 |
| 40 | Osteoarthritis and Cartilage 🔗 | 2007- | Clinical Key | 18 |
| 41 | Otolaryngologic Clinics of North America 🔗 | (2007-2014) | Clinical Key | 18 |
| 42 | Otolaryngology Case Reports 🔗 | 2016- | Clinical Key | 23 |
| 43 | Otology & Neurotology 🔗 | 2001- | Ovid | 17 |
| 44 | Oxford Medical Case Reports (OMCR) 🔗 | 2014- | Oxford | 19 |
| 45 | Oxford Open Immunology 🔗 | 2020- | Oxford | 20 |
