| Osna Géar | Other services | 2025 |
| Osney Island Boat Club Limited | Arts & recreation | 2000 |
| Osney Lane (Abbey Walk) Management Company Limited | Households | 1992 |
| Ospip Limited | Education | 2010 |
| Osprey Recovery Ltd | Wholesale & retail | 2024 |
| Osps Trustee Limited | Extraterritorial | 2012 |
| Ospt Ltd | Professional & scientific | 2019 |
| Ossl Limited | Wholesale & retail | 2010 |
| Ostin Construction Ltd | Construction | 2018 |
| OSU Group Ltd | Administrative & support | 2020 |
| Osusf Ltd | Education | 2020 |
| OT Projects Limited | Construction | 2010 |
| OT2 Managers Limited | Professional & scientific | 2015 |
| Otabu Certification Limited | Professional & scientific | 2023 |
| OTB Services Ltd | Information & communication | 2018 |
| OTG Ventures Ltd | Manufacturing | 2026 |
| Otheos.Com Limited | Wholesale & retail | 1999 |
| Otmoor Management Company Limited | Households | 2009 |
| OTO Enterprises Ltd | Other services | 1998 |
| Otrac Capital Limited | Financial services | 2022 |
| Otthonest Limited | Real estate | 2025 |
| Otto Digby-Dysart Ltd | Professional & scientific | 2025 |
| OUP Group Pension Trustee Limited | Professional & scientific | 2019 |
| Oupm Limited | Professional & scientific | 2021 |
| OUR Horizon Collective CIC | Education | 2019 |
| OUR Limited | Information & communication | 2026 |
| OUR Pages Limited | Professional & scientific | 2000 |
| OUR Tutor Education Limited | Education | 2016 |
| OUR Tutor Limited | Education | 2016 |
| Ourion Ltd | Information & communication | 2024 |
| Ourmanflint Limited | Other services | 2020 |
| Ourtutor Founders Limited | Education | 2011 |
| Oury Nicholsons & Co LLP | | 2022 |
| Ovada (Oxfordshire Visual Arts Development Agency) Limited | Arts & recreation | 2004 |
| Ovdom Properties Ltd | Real estate | 2020 |
| Oveg Holdings Limited | Financial services | 2024 |
| Overcoming Multiple Sclerosis | Health & social care | 2014 |
| Oving Road (Whitchurch) Management Company Ltd | Households | 2019 |
| Ovul Services Ltd | Information & communication | 2024 |
| Owen Greenings & Mumford (Holdings) Limited | Manufacturing | 2007 |
| Own That Build Ltd | Manufacturing | 2025 |
| Owning Your Future Ltd | Professional & scientific | 2012 |
| Ownyourai Ltd | Information & communication | 2025 |
| OX Brickwork Ltd | Construction | 2026 |
| OX Building Solutions Ltd | Construction | 2021 |
| OX Chauffeurs Ltd | Transport & logistics | 2025 |
| OX Hospitality Ltd | Wholesale & retail | 2021 |
| OX Legal Remedy Clinic Limited | Information & communication | 2024 |
| OX One Services Ltd | Wholesale & retail | 2023 |
| OX Psychology Group Ltd | Education | 2021 |
| OX Repairing Station Ltd | Other services | 2018 |
| OX Rides Ltd | Transport & logistics | 2026 |
| OX Shire Homes Ltd | Real estate | 2025 |
| OX SOX Limited | Other services | 2019 |
| OX Supply Co. Ltd | Professional & scientific | 2026 |
| OX Tailoring Limited | Other services | 2026 |
| OX Taxis Chauffeurs Ltd | Transport & logistics | 2024 |
| OX Taxis Ltd | Transport & logistics | 2023 |
| OX TEN Consulting Ltd | Professional & scientific | 2020 |
| Ox-Academic Summer-School Tours Ltd | Education | 2015 |
| Ox-Chiro Chiropractic Clinic Limited | Health & social care | 2021 |
| Ox-Fords Property Maintenance Limited | Administrative & support | 2024 |
| Ox-Fords Services Limited | Transport & logistics | 2022 |
| OX0C Energy Tech Limited | Professional & scientific | 2013 |
| OX1 Commercial Ltd | Real estate | 2019 |
| OX1 Developments Limited | Real estate | 2026 |
| OX1 Freehold Management Ltd | Administrative & support | 2017 |
| OX1 Group Ltd | Real estate | 2018 |
| OX1 Limited | Real estate | 2011 |
| OX1 Residential 10 Ltd | Real estate | 2018 |
| OX1 Residential 11 Ltd | Real estate | 2021 |
| OX1 Residential 12 Ltd | Real estate | 2021 |
| OX1 Residential 14 Ltd | Real estate | 2024 |
| OX1 Residential 15 Ltd | Real estate | 2024 |
| OX1 Residential 16 Ltd | Real estate | 2024 |
| OX1 Residential 17 Ltd | Real estate | 2024 |
| OX1 Residential 18 Ltd | Real estate | 2024 |
| OX1 Residential 19 Ltd | Real estate | 2024 |
| OX1 Residential 2 Ltd | Real estate | 2016 |
| OX1 Residential 20 Ltd | Real estate | 2024 |
| OX1 Residential 3 Ltd | Real estate | 2016 |
| OX1 Residential 4 Ltd | Real estate | 2016 |
| OX1 Residential 5 Ltd | Real estate | 2016 |
| OX1 Residential 6 Ltd | Real estate | 2018 |
| OX1 Residential 7 Ltd | Real estate | 2018 |
| OX1 Residential 8 Ltd | Real estate | 2018 |
| OX1 Residential 9 Ltd | Real estate | 2018 |
| OX2 Consulting Limited | Professional & scientific | 2010 |
| OX33 Ltd | Construction | 2025 |
| OX4 LVN Limited | Manufacturing | 2025 |
| OX4 Nails & Beauty Ltd | Other services | 2021 |
| OX4 Properties Limited | Real estate | 2002 |
| OX4D Advertising Ltd | Professional & scientific | 2023 |
| OX5 Consultancy Limited | Real estate | 2011 |
| OXA Autonomy Ltd | Information & communication | 2014 |
| Oxai Ltd | Information & communication | 2026 |
| Oxailis Ltd | Information & communication | 2025 |
| Oxarch Technical Services Limited | Professional & scientific | 2000 |
| Oxbp Limited | Information & communication | 2023 |
| Oxbrew Ltd | Manufacturing | 2023 |