| Outwood Office Opportunities Ltd | Administrative & support | 2008 |
| Ovagate Limited | Professional & scientific | 2010 |
| Oval (2041) Limited | Professional & scientific | 2005 |
| Oval (2042) Limited | Professional & scientific | 2005 |
| Oval (2304) Limited | Information & communication | 2018 |
| Oval Marketing Limited | Professional & scientific | 2019 |
| Oval UK Holdings Limited | Financial services | 2021 |
| Ovalhouse Limited | Arts & recreation | 1983 |
| Ovaws Trading Ltd | Wholesale & retail | 2023 |
| Over Speed Enterprises Ltd | Transport & logistics | 2025 |
| Over the Sea Limited | Arts & recreation | 2018 |
| Overdale (UK) Limited | Real estate | 2014 |
| Overdale Property Management Limited | Households | 1987 |
| Overdales Legal Limited | Financial services | 2010 |
| Overend Group Ltd | Wholesale & retail | 2025 |
| Overexbosed Ltd | Wholesale & retail | 2020 |
| Overford Limited | Professional & scientific | 2021 |
| Overland Discovery Expo Ltd | Administrative & support | 2025 |
| Overland Rentals Limited | Households | 2024 |
| Overlap Associates (UK) Limited | Administrative & support | 2018 |
| Overpowered Nutrition Ltd | Wholesale & retail | 2025 |
| Overprinting Machines (UK) Limited | Manufacturing | 2011 |
| Overseas Education Services UK Ltd | Education | 2022 |
| Overseas Group of Education Services Ltd | Education | 2024 |
| Overseas Trading Limited | Wholesale & retail | 2002 |
| Overseas VM Limited | Extraterritorial | 2013 |
| Overstone Lodge Management Limited | Administrative & support | 1997 |
| Overstone Park Limited | Hospitality | 1997 |
| Overstone Property Group Limited | Financial services | 2020 |
| Overstone Resort Holdings Limited | Hospitality | 2017 |
| Overtimeflex JOB Seekers Recruitment Limited | Administrative & support | 2025 |
| Overwatch Training Solutions Ltd | Education | 2022 |
| Ovesh Umar Ltd | Wholesale & retail | 2025 |
| Ovolo Building Consultancy Ltd | Professional & scientific | 2019 |
| Owen & Co Property Investments Limited | Real estate | 2025 |
| Owen Armstrong Rail Ltd | Construction | 2019 |
| Owen Management Ltd | Professional & scientific | 2026 |
| Owen on the Rhodes Ltd | Wholesale & retail | 2024 |
| Owen Tattooing Ltd | Other services | 2023 |
| OWL BEE Limited | Information & communication | 2018 |
| OWL GAS Services Limited | Construction | 2021 |
| OWL Insights Ltd | Information & communication | 2026 |
| OWL Investigations Ltd | Administrative & support | 2016 |
| OWL Tuition Ltd | Education | 2023 |
| Owlett Fishing Limited | Transport & logistics | 2011 |
| Owllet Limited | Real estate | 2007 |
| Owls Healthcare Ltd | Health & social care | 2018 |
| Owls Kind Occupy Ltd | Professional & scientific | 2024 |
| OWM Limited | Financial services | 2021 |
| Ownership at Work | Other services | 1984 |
| Ownestproperty Ltd | Real estate | 2024 |
| Owningit Limited | Professional & scientific | 2023 |
| Ownpath Recruitment Ltd | Professional & scientific | 2026 |
| OWT Ltd | Hospitality | 2018 |
| Oxclose Road Limited | Professional & scientific | 2020 |
| Oxeye Properties Ltd | Real estate | 2026 |
| Oxford City Energy Network Limited | Construction | 2025 |
| Oxford Court (Guiseley) Management Company Limited | Real estate | 2005 |
| Oxford Energy Network Limited | Construction | 2024 |
| Oxford Grammar School Limited | Extraterritorial | 2013 |
| Oxford Road Ltd | Real estate | 2024 |
| Oxford Tutors Ltd | Education | 2022 |
| Oxley & Co Consultants Ltd | Professional & scientific | 2021 |
| Oxley Group Holdings Ltd | Wholesale & retail | 2021 |
| Oxley Sign Installations Ltd | Administrative & support | 2017 |
| Oxonox Commercial Ltd | Professional & scientific | 2020 |
| Oxonox Limited | Professional & scientific | 2020 |
| Oxxie Ltd | Information & communication | 2018 |
| Oxygen Bubbles Limited | Information & communication | 2026 |
| Oxygen Data Media Ltd | Information & communication | 2016 |
| Oxygen Enterprise Partners Ltd | Other services | 2012 |
| Oxygen Films (II) CIC | Information & communication | 2019 |
| Oxylus Limited | Real estate | 2020 |
| OY Fuels Limited | Wholesale & retail | 2026 |
| OYA Living Ltd | Real estate | 2022 |
| Oyea Tech Ltd | Wholesale & retail | 2021 |
| Oyelams Consulting Ltd | Financial services | 2011 |
| Oyibode 12 Limited | Health & social care | 2022 |
| Oynx Secure Solutions Ltd | Administrative & support | 2025 |
| OZ Emenike Healthcare Services Limited | Health & social care | 2019 |
| OZAR1910 Ltd | Education | 2025 |
| Oziomachi Ltd | Professional & scientific | 2025 |
| Ozksm Limited | Professional & scientific | 2020 |
| Ozman Electrical Ltd | Construction | 2025 |
| Ozmo Entertainment Limited | Extraterritorial | 2004 |
| Ozola Ltd | Professional & scientific | 2025 |
| Ozone Goods Ltd | Wholesale & retail | 2024 |
| Oztrad Medix Ltd | Wholesale & retail | 2024 |
| Ozymandias Holdings | Financial services | 2018 |
| Ozyurt Ltd | Wholesale & retail | 2023 |
| P & a Properties Services Ltd | Other services | 2017 |
| P & B Metal Components Limited | Manufacturing | 1961 |
| P & C M Engineering Services Ltd | Manufacturing | 2016 |
| P & D Knight Limited | Construction | 2026 |
| P & J Helm Property Investments Ltd | Real estate | 2018 |
| P & J Professional Consultants Ltd | Health & social care | 2016 |
| P & K Soni Ltd | Wholesale & retail | 2021 |
| P & L Holdings Inc Limited | Administrative & support | 2007 |
| P & M Group Holdings Limited | Financial services | 2024 |
| P & M Harrison Holdings Limited | Real estate | 2017 |