| OUR Lady of Peace Catholic Club Limited | Hospitality | 1997 |
| OUR Lady Seat of Wisdom | Education | 2012 |
| OUR Lady's | Education | 2012 |
| OUR Land Limited | Information & communication | 2022 |
| OURG4R4GE Ltd | Wholesale & retail | 2024 |
| Oursoul Tower Limited | Real estate | 2014 |
| Ouse Road MOT Limited | Wholesale & retail | 2021 |
| OUT of the Archive CIC | Arts & recreation | 2019 |
| OUT of the Box Services Ltd | Health & social care | 2015 |
| OUT of the Cave Ltd | Information & communication | 2011 |
| Outcome Oasis Learning Ltd | Education | 2024 |
| Outdoor Animal-Assisted Therapy Services Ltd | Health & social care | 2025 |
| Outdoor Animal-Facilitated Therapy Services (Oats) CIC | Agriculture & fishing | 2023 |
| Outdoors Thinking Ltd | Education | 2020 |
| Outlaw Motorsport Ltd | Wholesale & retail | 2015 |
| Outlier Education Limited | Education | 2022 |
| Outline Communication Ltd | Energy | 2024 |
| Outline Construction Ltd | Construction | 2018 |
| Outofthebox Training & Consultancy | Education | 2021 |
| Outokumpu Stainless Limited | Manufacturing | 1993 |
| Outokumpu Stainless UK Research Foundation Ltd | Education | 1995 |
| Outreach and Welfare Services Ltd | Education | 2013 |
| Outright Padel Ltd | Arts & recreation | 2026 |
| Outside Design Limited | Administrative & support | 2010 |
| Outside Strategy Ltd | Administrative & support | 2025 |
| Outsurs Group Ltd | Transport & logistics | 2025 |
| Outta National Couriers Limited | Transport & logistics | 2023 |
| Outtatime Logistics Limited | Transport & logistics | 2025 |
| OV Transport Ltd | Transport & logistics | 2023 |
| OVA Heat Limited | Construction | 2022 |
| Oval Consortium Limited | Hospitality | 2016 |
| Ovarro DA Holdings Ltd | Professional & scientific | 1997 |
| Ovarro DA Ltd | Professional & scientific | 1983 |
| Ovarro Group Limited | Financial services | 2019 |
| Ovarro Holdings Ltd | Financial services | 2018 |
| Ovarro LD Ltd | Manufacturing | 1994 |
| Ovarro Ltd | Financial services | 2013 |
| Ovarro TS Ltd | Information & communication | 2009 |
| Oven Revive Limited | Administrative & support | 2010 |
| Over and Above Brands LLP | | 2015 |
| Over the Bridge Shop Ltd | Wholesale & retail | 2025 |
| Over the Yardarm Ltd | Hospitality | 2021 |
| Overall Deal Limited | Hospitality | 2014 |
| Overdale Farms Limited | Agriculture & fishing | 2005 |
| Overdrive Repair Services Ltd | Manufacturing | 2012 |
| Overeye Ltd | Professional & scientific | 2016 |
| Overflowing Life Ministries Limited | Other services | 2006 |
| Overhead Crane Services UK Ltd | Professional & scientific | 2019 |
| Overheating Solutions Ltd | Professional & scientific | 2025 |
| Override Events Limited | Administrative & support | 2026 |
| Overton Group Limited | Administrative & support | 2015 |
| OVI Car Body Repair Limited | Wholesale & retail | 2014 |
| OVI Car Maintenance Ltd | Wholesale & retail | 2025 |
| OVO Kitchen Limited | Hospitality | 2025 |
| OVO Properties Ltd | Real estate | 2023 |
| OVY Haulage Ltd | Transport & logistics | 2025 |
| OW Roofing Services Ltd | Construction | 2025 |
| Owais Holding Ltd | Transport & logistics | 2021 |
| Owen Joseph Limited | Construction | 2013 |
| Owen Portfolio Ltd | Financial services | 2018 |
| Owen Springs Limited | Manufacturing | 2004 |
| Owens Medical Services Limited | Health & social care | 2022 |
| OWL Industries Limited | Financial services | 2022 |
| OWL Surveys Ltd | Professional & scientific | 2024 |
| OWL74 Ltd | Health & social care | 2018 |
| Owled Limited | Wholesale & retail | 2016 |
| Owler LEE Developments Limited | Real estate | 2016 |
| Owls Hospitality Limited | Hospitality | 2025 |
| Owlthorpe Electrical Services Limited | Construction | 2024 |
| OWS Management Limited | Administrative & support | 2026 |
| Oxbridge Psychometrics Ltd | Professional & scientific | 2023 |
| Oxcroft Commercial Finance Limited | Financial services | 2021 |
| Oxcroft Financial Services Ltd | Financial services | 2019 |
| Oxelectrical Ltd | Construction | 2017 |
| Oxer Aviation Ltd | Transport & logistics | 2016 |
| Oxford & Cambridge Properties Ltd | Real estate | 2021 |
| Oxford Dance Camp Limited | Arts & recreation | 2010 |
| Oxford Operations Management Ltd | Hospitality | 2025 |
| Oxford Pools Limited | Construction | 2005 |
| Oxford Union Elevator Company Limited | Wholesale & retail | 2025 |
| Oxhorn Limeworks Limited | Construction | 2023 |
| Oxphen Premium Management Ltd | Construction | 2022 |
| Oxspring Design Limited | Professional & scientific | 2017 |
| Oxspring Investments Limited | Manufacturing | 2022 |
| Oxspring Network Solutions Limited | Information & communication | 2000 |
| Oxspring Toddler Group Ltd | Education | 2002 |
| Oxspring United Junior Football Club Limited | Arts & recreation | 2026 |
| Oxton Consulting Limited | Real estate | 2008 |
| Oxton Technologies Ltd | Professional & scientific | 2007 |
| OXY Hbot Limited | Health & social care | 2025 |
| Oxygenesis Limited | Health & social care | 2025 |
| Oxyhealthcare Holdings Ltd | Health & social care | 2025 |
| Oxyhealthcare Limited | Health & social care | 2024 |
| Oxyhealthcare Solutions Ltd | Health & social care | 2025 |
| Oxylife Limited | Health & social care | 2025 |
| Oxyshop Limited | Wholesale & retail | 2005 |
| OY Ventures Ltd | Professional & scientific | 2024 |
| OYA Collection Limited | Wholesale & retail | 2025 |
| Oyster Developments Ltd | Construction | 2026 |
| Oyster Wealth Planning Limited | Financial services | 2019 |