| Orangestripe Telecom Ltd | Information & communication | 2002 |
| Orba Technologies Ltd | Information & communication | 2026 |
| Orchard Farm (Bucks) Ltd | Agriculture & fishing | 2017 |
| Orchard House (High Wycombe) Ltd | Households | 1989 |
| Orchard Place (Penn) Residents Management Company Limited | Households | 2016 |
| Orcro Holdings Limited | Financial services | 2024 |
| Orcro Limited | Professional & scientific | 2018 |
| ORD & SON Limited | Information & communication | 2019 |
| Oregon Audio Visual Services Ltd | Professional & scientific | 2014 |
| Orford Enterprises Limited | Real estate | 2022 |
| Orga Property Group Limited | Construction | 2022 |
| Orgment Limited | Professional & scientific | 2003 |
| Origin Frames Limited | Manufacturing | 2002 |
| Origin Powder Coating Limited | Manufacturing | 2023 |
| Orion B Services Limited | Construction | 2023 |
| Orran Partners Limited | Professional & scientific | 2013 |
| Orwell Trucks Limited | Extraterritorial | 1991 |
| Oryx Engineering Limited | Professional & scientific | 2018 |
| Oryx Groundcare Ltd. | Administrative & support | 2011 |
| Oski Marketing Ltd | Wholesale & retail | 2020 |
| Osmotics Consulting Ltd | Professional & scientific | 2020 |
| Osnik Ltd | Construction | 2022 |
| OSR Services Limited | Administrative & support | 2024 |
| Oswiftly Limited | Professional & scientific | 2022 |
| OTB Vending Ltd | Wholesale & retail | 2025 |
| Otii Limited | Construction | 2011 |
| Otwpms Limited | Professional & scientific | 2013 |
| OUR IT Team Ltd | Information & communication | 2014 |
| OUR Orchard Ltd | Agriculture & fishing | 2025 |
| Ourtime Children`S Services Ltd | Health & social care | 2008 |
| Outlet Choice Ltd | Wholesale & retail | 2025 |
| Outstanding Ltd | Education | 2011 |
| Oven Ready Limited | Administrative & support | 2007 |
| Over 65 Projects Limited | Extraterritorial | 2022 |
| Overleigh Court Residents Association Limited | Households | 1974 |
| Overs Farm Residents Company Limited | Households | 2002 |
| Owaifa Consultancy Limited | Professional & scientific | 2021 |
| Owca Limited | Information & communication | 2025 |
| OWL Technical Services Limited | Information & communication | 2012 |
| Oxbucks Services Ltd | Construction | 2024 |
| Oxby Recruitment Limited | Administrative & support | 2025 |
| Oxentyx Limited | Wholesale & retail | 2026 |
| Oxford College of Education Ltd | Education | 2017 |
| Oxford Designers Ltd | Information & communication | 2024 |
| Oxford Instruments AFM Limited | Professional & scientific | 1978 |
| Oxford Instruments Holdings Europe Limited | Professional & scientific | 2009 |
| Oxford Instruments Industrial Products Holdings Limited | Professional & scientific | 2000 |
| Oxford Instruments Industrial Products Limited | Manufacturing | 1972 |
| Oxford Instruments Molecular Biotools Limited | Manufacturing | 2003 |
| Oxford Instruments Nanotechnology Tools Holdings Limited | Professional & scientific | 2000 |
| Oxford Instruments Nanotechnology Tools Limited | Manufacturing | 1961 |
| Oxford Instruments Overseas Holdings 2008 Limited | Professional & scientific | 2008 |
| Oxford Instruments Overseas Holdings Limited | Professional & scientific | 1997 |
| Oxford Instruments Overseas Marketing Limited | Administrative & support | 1989 |
| Oxford Instruments Pension Trustee Limited | Administrative & support | 1996 |
| Oxford Instruments PLC | Professional & scientific | 1963 |
| Oxford Instruments UK 2013 Limited | Financial services | 2013 |
| Oxfordshire Executive Limited | Transport & logistics | 2024 |
| OXO Travels Limited | Administrative & support | 2024 |
| Oxon Deer Limited | Agriculture & fishing | 2018 |
| Oxpens Ltd | Wholesale & retail | 2025 |
| Oxtech AI Ltd | Information & communication | 2025 |
| Oxton Ltd | Information & communication | 2022 |
| OYE Holdens Limited | Real estate | 2015 |
| Ozzydeem Ltd | Professional & scientific | 2025 |
| P & J Cleaning Services Ltd | Administrative & support | 2004 |
| P & J Roofing & Building Contractors Ltd | Construction | 2006 |
| P & N Cartons Limited | Professional & scientific | 2005 |
| P & W Commercials Limited | Wholesale & retail | 2004 |
| P a Cook & Co (High Wycombe) Ltd | Professional & scientific | 2010 |
| P Carr Construction Ltd | Construction | 2025 |
| P Courtney Ltd | Professional & scientific | 2009 |
| P D Brooks Limited | Other services | 2003 |
| P I Buchanan Limited | Professional & scientific | 2018 |
| P J Lickley Carpentry Ltd | Construction | 2003 |
| P&H Living Ltd | Real estate | 2018 |
| P&J Hazell Ltd | Wholesale & retail | 2021 |
| P&P Connect Ltd | Transport & logistics | 2025 |
| P&S Installers Limited | Manufacturing | 2026 |
| P.J Painting & Decoration Ltd | Construction | 2025 |
| P.L.Blake Limited | Professional & scientific | 1985 |
| P.Mcg Management Ltd | Information & communication | 2023 |
| P.S.B. Builders Ltd | Construction | 2007 |
| P20 Holdings Ltd | Other services | 2023 |
| P21 Holdings Ltd | Real estate | 2025 |
| P3 Services Ltd | Other services | 2022 |
| P30 Property Ltd | Real estate | 2020 |
| PA Window and Door Ltd | Construction | 2025 |
| Pacelrus Limited | Transport & logistics | 2018 |
| Pacemake Group Ltd | Financial services | 2023 |
| Pacemake Limited | Construction | 2015 |
| Pacet Limited | Manufacturing | 2013 |
| Packaged Sounds Group Limited | Administrative & support | 2014 |
| Packaged Sounds Ltd | Administrative & support | 2017 |
| Paclo Ltd | Professional & scientific | 2025 |
| Padda Investment Ltd | Real estate | 2017 |
| Paddleboard UK Ltd | Wholesale & retail | 2021 |
| Page Turner Media Ltd | Information & communication | 2026 |
| PAH Developments Limited | Construction | 2018 |
| Paige & Lacey Limited | Hospitality | 2019 |