| Mvmnt Functional Fitness Ltd | Arts & recreation | 2020 |
| My Mojo Zone Ltd | Education | 2022 |
| Mystery INK Ltd | Information & communication | 2024 |
| N & K Estates Ltd | Construction | 2026 |
| N E Gannon Limited | Construction | 2007 |
| N Greenaway Construction Ltd | Construction | 2026 |
| N J F Electrical Services Limited | Construction | 2019 |
| Nadeem Saeed Ltd | Health & social care | 2011 |
| Nail Products Ltd | Other services | 2020 |
| Narrow Lane Developments Limited | Real estate | 2022 |
| Nationwide Vehicle Transport Limited | Transport & logistics | 2014 |
| Navidea Biopharmaceuticals Limited | Professional & scientific | 2011 |
| Navigating Choices Ltd | Professional & scientific | 2023 |
| NBH Solutions Limited | Information & communication | 2019 |
| Neika Ltd | Administrative & support | 2021 |
| Neil Gibson Consulting Limited | Professional & scientific | 2017 |
| Neutral Human Limited | Administrative & support | 2021 |
| New Lucky Chen Limited | Hospitality | 2026 |
| New Page Aviation Ltd | Transport & logistics | 2022 |
| Newbarn Close (Thame) Management Company Limited | Households | 2006 |
| Nexorium Ltd | Wholesale & retail | 2025 |
| Nexus SPR Innovations Limited | Professional & scientific | 2024 |
| Nicholson Brown Limited | Financial services | 2014 |
| Nico Industrial Services U.K. Ltd | Manufacturing | 2015 |
| Nicola Richardson Architects Ltd | Professional & scientific | 2016 |
| Niem Automotive Limited | Financial services | 2022 |
| Nightingale and Sons Oxford Joinery Limited | Construction | 2026 |
| Nilsam Ltd | Financial services | 2026 |
| NJM Construction Consultants Limited | Extraterritorial | 2020 |
| NO1 Illume Ltd | Wholesale & retail | 2020 |
| Nodwell Ownership Ltd | Real estate | 2017 |
| Nooboo Marketing Ltd | Professional & scientific | 2017 |
| North Hinksey Construction Limited | Construction | 2004 |
| North Oxford Homes Limited | Real estate | 2016 |
| Note House Investments Ltd | Real estate | 2018 |
| Novas Partners Ltd | Professional & scientific | 2023 |
| Novoro Ltd | Financial services | 2025 |
| NOW Consult Ltd | Professional & scientific | 2015 |
| NT Lighting Services Limited | Information & communication | 2021 |
| Oak House Wills & Estate Planning Ltd | Professional & scientific | 2021 |
| Oak Taverns Limited | Hospitality | 1991 |
| Oak Tree Landscaping Limited | Administrative & support | 2021 |
| Oakcroft Consulting Limited | Information & communication | 2014 |
| Oakley Foods Ltd | Hospitality | 2018 |
| Oakley Organics Ltd | Hospitality | 2018 |
| Oaksteer Advisory Ltd | Professional & scientific | 2025 |
| OCC Psychs (London) Limited | Health & social care | 2017 |
| Occasio Insights Ltd | Information & communication | 2024 |
| OCD Paintwork Limited | Wholesale & retail | 2025 |
| Ochestra Technologies Limited | Information & communication | 2024 |
| Oculomex Health Ltd | Information & communication | 2024 |
| Oculorum Ltd | Professional & scientific | 2018 |
| Office for Oversight Ltd | Professional & scientific | 2021 |
| Official Business Ltd | Professional & scientific | 2018 |
| OH Studio Ltd | Information & communication | 2018 |
| OIL Tank Solutions Ltd | Extraterritorial | 2009 |
| Oio.Studio Ltd | Professional & scientific | 2019 |
| OJ Productions Limited | Information & communication | 2018 |
| OJM Estates Limited | Real estate | 2024 |
| Okeeffe Consultancy Limited | Information & communication | 2026 |
| Old Maltings Residents Association Limited(The) | Households | 1983 |
| Olive Green House & Garden Limited | Construction | 2025 |
| Oliver Bartman | Education | 2021 |
| Oliver Smith Engineering Limited | Professional & scientific | 2020 |
| Ollie Tiong Limited | Information & communication | 2015 |
| Omfi Tech Ltd | Information & communication | 2026 |
| ON Your Boat Ltd | Wholesale & retail | 2021 |
| One Red Mouse Limited | Information & communication | 2014 |
| Opal Ecom Limited | Professional & scientific | 2025 |
| Openscript CIC | Arts & recreation | 2022 |
| Opium Arts Management Services Limited | Professional & scientific | 2019 |
| Oppa Gang Ltd | Hospitality | 2025 |
| Opteven Dealer UK Ltd | Financial services | 2009 |
| Opteven Holdings UK Ltd | Professional & scientific | 2009 |
| Opteven Insured UK Ltd | Financial services | 2003 |
| Opteven Services UK Ltd | Financial services | 2017 |
| Opteven UK Limited | Administrative & support | 2016 |
| Optical Filters Limited | Manufacturing | 1988 |
| Opticonsultancy Limited | Information & communication | 2009 |
| Optimal Currency Limited | Financial services | 2018 |
| Optimal Performance Ltd | Professional & scientific | 2020 |
| Optimus Therapeutic Technologies Limited | Professional & scientific | 2018 |
| Oracle EAR Care Ltd | Health & social care | 2020 |
| Orafinapps Limited | Administrative & support | 2005 |
| Orange Circle Limited | Real estate | 2001 |
| Orbit FAB Ltd | Manufacturing | 2022 |
| Orchard Farm of Oxford Limited | Agriculture & fishing | 2023 |
| Orchard Therapeutic Farm Ltd | Education | 2021 |
| Orchard View Rentals Ltd | Real estate | 2020 |
| Orcs Properties Limited | Real estate | 2024 |
| Origin Effects Limited | Manufacturing | 2014 |
| Ormsdale Associates Ltd | Administrative & support | 2024 |
| Osteopathics (HRH) Ltd | Health & social care | 2011 |
| Otherwise Studio Ltd | Professional & scientific | 2023 |
| Otto & Greening Ltd | Wholesale & retail | 2014 |
| Outside Tech Ltd | Professional & scientific | 2021 |
| Ovation Systems Limited | Manufacturing | 1987 |
| Overland Design and Build Limited | Professional & scientific | 2014 |
| Ovivio Limited | Extraterritorial | 2025 |
| Owlswick Properties Limited | Construction | 2001 |