| Oasis Private Care Limited | Administrative & support | 2009 |
| Obcessr Ltd | Information & communication | 2019 |
| Oceanlore Ltd | Real estate | 2026 |
| Ocsrc Ltd | Professional & scientific | 2017 |
| Octopus Events Limited | Administrative & support | 2016 |
| OD Plumbing & Heating Ltd | Construction | 2021 |
| Odonata Limited | Administrative & support | 2019 |
| OFF Record Limited | Information & communication | 2025 |
| Offa Network Ltd | Administrative & support | 2024 |
| Offshore Crewing Specialists Limited | Administrative & support | 2020 |
| OLA4K1000 Ltd | Health & social care | 2020 |
| Old Harvest Land Limited | Real estate | 1996 |
| Old Police Station Management Company Limited | Households | 1992 |
| Old Smithy Didcot Limited | Households | 2011 |
| Olia Ltd | Professional & scientific | 2020 |
| Omega Prime Limited | Hospitality | 1998 |
| ONI Cole Limited | Administrative & support | 2022 |
| Only Vans 4 U Ltd | Wholesale & retail | 2025 |
| Onview.Net Limited | Information & communication | 1998 |
| Open House Vowh Ltd | Real estate | 2025 |
| Oppo Coaching Ltd | Professional & scientific | 2024 |
| Opteamise Ltd | Health & social care | 2021 |
| Optijan Digital Limited | Professional & scientific | 2019 |
| Optima Business Services Ltd. | Professional & scientific | 1998 |
| OR Group Ltd | Manufacturing | 2023 |
| Orangephase Global Ltd | Wholesale & retail | 2026 |
| Orbus Limited | Real estate | 1999 |
| Orchard House Clinic Wantage Limited | Health & social care | 2011 |
| Orga M&C Ltd | Professional & scientific | 2015 |
| OS Therapies UK Ltd | Manufacturing | 2025 |
| Oskar Network Ltd | Information & communication | 2023 |
| OSR Telecoms Ltd | Information & communication | 2023 |
| Osteopathic Centre for Animals Limited | Education | 2014 |
| Otter Property Limited | Real estate | 2018 |
| Outside the Box Finance Limited | Financial services | 2010 |
| Overreach Barbell Ltd | Arts & recreation | 2021 |
| OX & Vale Vintage Ltd | Wholesale & retail | 2026 |
| OX12 Technologies Limited | Information & communication | 2013 |
| Oxford Authentication Limited | Professional & scientific | 1997 |
| Oxford CARE4YOU Ltd | Health & social care | 2025 |
| Oxford Clinical Psychology Limited | Health & social care | 2016 |
| Oxford Close (Kingston Bagpuize) Management Company Limited | Households | 2021 |
| Oxford Club Promo Ltd | Professional & scientific | 2026 |
| Oxford Diocesan Schools Trust | Education | 2012 |
| Oxford Events Limited | Hospitality | 2015 |
| Oxford Flour Mill Ltd | Manufacturing | 2023 |
| Oxford Hens Films Limited | Financial services | 2007 |
| Oxford International Biomedical Enabling Centre Ltd | Professional & scientific | 2024 |
| Oxford International Exchange Ltd. | Administrative & support | 1999 |
| Oxford Medicolegal Services Limited | Health & social care | 2025 |
| Oxford Menopause Ltd | Health & social care | 2021 |
| Oxford Movies Limited(The) | Real estate | 1983 |
| Oxford Online Education Ltd | Education | 2021 |
| Oxford Philharmonic Orchestra Productions Limited | Education | 1998 |
| Oxford Philharmonic Orchestra Trust | Education | 1998 |
| Oxford Smart Homes Ltd | Energy | 2022 |
| Oxford Visionary Ltd | Information & communication | 2022 |
| Oxfordshire Arts Trading Limited | Education | 2014 |
| Oxfordshire Bakery Ltd | Manufacturing | 2025 |
| Oxfordshire Collectibles Ltd | Wholesale & retail | 2018 |
| Oxfordshire Drain Services Limited | Water & waste | 2013 |
| Oxfordshire Health & Safety Ltd | Professional & scientific | 2022 |
| Oxfordshire Master Thatchers Ltd | Construction | 2021 |
| Oxon Research Ltd | Administrative & support | 2008 |
| P J Carter Limited | Construction | 1999 |
| P Wakefield Utilities Ltd | Construction | 2026 |
| P&L Accountancy and Bookkeeping Limited | Professional & scientific | 2013 |
| P&M Cleaning Experts Ltd | Construction | 2025 |
| P-Dynasty Ltd | Hospitality | 2024 |
| P. D. C. R. Limited | Administrative & support | 2011 |
| P.F.I. Cole Limited | Arts & recreation | 1976 |
| P.J.E. Building Contractors Limited | Construction | 2013 |
| P.O.A -Plus Courier and Logistics Company Limited | Transport & logistics | 2024 |
| P.T. Hannaby (Builders & Decorators) Limited | Construction | 1974 |
| P.V. MAC Limited | Administrative & support | 2012 |
| Pain Free IT Ltd | Information & communication | 2011 |
| Paladin Leisure Limited | Arts & recreation | 2003 |
| Palena Limited | Information & communication | 2026 |
| PAN Cook House Limited | Hospitality | 2019 |
| Panda Healthcare Limited | Health & social care | 2022 |
| Panthera Limited | Professional & scientific | 1999 |
| Papaya Property Limited | Professional & scientific | 2005 |
| Papson Music Limited | Arts & recreation | 2024 |
| Paradise Island Consulting Limited | Information & communication | 2017 |
| Paradiso Ventures Limited | Real estate | 2025 |
| Pareva UK Ltd | Information & communication | 2024 |
| Park END Design Ltd | Professional & scientific | 2014 |
| Parker & Warne Vehicle Services Limited | Wholesale & retail | 2011 |
| Parklane Driveways Ltd | Construction | 2009 |
| Parlour Brew Company Limited | Manufacturing | 2026 |
| Parsons Place Freehold Limited | Households | 2023 |
| Particular Limited | Hospitality | 2014 |
| Partner Investment Club Assisted Living Investments LP | | 2026 |
| Password Productions Ltd. | Arts & recreation | 2006 |
| Patrick Gilmore Consultants Limited | Professional & scientific | 2018 |
| Paul Clark Creative Limited | Professional & scientific | 2020 |
| Paul Merriman Design Ltd | Arts & recreation | 2013 |
| Paul Robins Promotions Ltd | Arts & recreation | 2018 |
| Paul's Windows Limited | Other services | 2022 |
| Payblink Ltd | Wholesale & retail | 2025 |