| Overmannow Limited | Health & social care | 1973 |
| Oversands Limited | Extraterritorial | 2009 |
| Overseas Commerce Agency LLP | | 2021 |
| Overseas Service & Management Ltd | Professional & scientific | 2021 |
| Overseas Technical Support Limited | Wholesale & retail | 2024 |
| Overt Security Limited | Administrative & support | 2018 |
| Overt Trade Ltd | Wholesale & retail | 2020 |
| Overwatch Emea UK Ltd | Construction | 2025 |
| Overwell WAN Limited | Wholesale & retail | 2023 |
| Ovexa Sols Limited | Information & communication | 2026 |
| OVI Spanu Ltd | Construction | 2014 |
| Ovid Consultancy Ltd | Professional & scientific | 2026 |
| Ovington Court Maintenance Limited | Real estate | 1981 |
| Ovion Ltd | Professional & scientific | 2019 |
| Ovrine Ltd | Wholesale & retail | 2025 |
| OVW Consultancy Ltd | Hospitality | 2024 |
| OW Financial Services Ltd | Professional & scientific | 2023 |
| OW Percussion Limited | Arts & recreation | 2014 |
| OW Supermart Ltd | Wholesale & retail | 2025 |
| OWA Properties Ltd | Real estate | 2022 |
| Owain Daniel John Doull Ltd | Arts & recreation | 2014 |
| Owain Gillard Locations & Media Ltd | Professional & scientific | 2024 |
| Owain Productions Limited | Arts & recreation | 2025 |
| Owen Associates Limited | Professional & scientific | 2015 |
| Owen Construction & Landscaping Ltd | Construction | 2018 |
| Owen Ecom Ltd | Wholesale & retail | 2025 |
| Owen Edwards Guitar Ltd | Other services | 2014 |
| Owen Edwards Music Ltd | Other services | 2014 |
| Owen Mobility Services Ltd | Education | 2026 |
| Owen Smith Builders Limited | Construction | 2012 |
| Owendo Incorporation Ltd | Information & communication | 2025 |
| Owings Limited | Professional & scientific | 2017 |
| OWL Farm Ltd | Information & communication | 2024 |
| OWL Management Limited | Professional & scientific | 2023 |
| OWL on Tree Ltd | Real estate | 2019 |
| OWL Property Management Ltd | Real estate | 2016 |
| Owlite Limited | Wholesale & retail | 2025 |
| Owne Limited | Financial services | 2017 |
| Owner Digital Ltd | Wholesale & retail | 2024 |
| OWO and Sons MA Ltd | Construction | 2023 |
| Owodele Investment UK Ltd | Wholesale & retail | 2019 |
| Owona Global Consulting Services Limited | Information & communication | 2017 |
| Owtan Limited | Information & communication | 2021 |
| Owtsl Mart Ltd | Wholesale & retail | 2025 |
| OX House Ltd | Information & communication | 2023 |
| Oxademy Ltd | Administrative & support | 2014 |
| Oxcloth Limited | Wholesale & retail | 2016 |
| Oxdelta Ltd | Information & communication | 2026 |
| Oxford AI Ltd | Information & communication | 2015 |
| Oxford CS Ltd | Construction | 2018 |
| Oxford Education Data LAB Ltd | Professional & scientific | 2022 |
| Oxford Elite Limited | Education | 2005 |
| Oxford Financial Ltd. | Financial services | 2025 |
| Oxford Flooring Limited | Wholesale & retail | 2012 |
| Oxford Odyssey Ltd | Wholesale & retail | 2024 |
| Oxford Persian Ltd | Education | 2013 |
| Oxford Room Lets Ltd | Real estate | 2017 |
| Oxford Scientific Ltd | Wholesale & retail | 2022 |
| Oxford Technologies Ltd | Information & communication | 2014 |
| Oxfordshire Garden Rooms Ltd | Construction | 2020 |
| Oxfordshire Paving Limited | Construction | 2017 |
| Oxfox Ltd | Other services | 2016 |
| Oxmore Holdings Ltd | Information & communication | 2018 |
| Oxons Midlands Ltd | Information & communication | 2024 |
| Oxygen People Limited | Administrative & support | 2016 |
| Oxygene Consulting UK Limited | Administrative & support | 2018 |
| Oxygene Properties Limited | Real estate | 2024 |
| Oxyile Corporation Ltd | Financial services | 2025 |
| Oyesiku Foods Ltd | Wholesale & retail | 2026 |
| Oyins Divine Ltd | Wholesale & retail | 2019 |
| Oyster Box Homes Ltd | Real estate | 2021 |
| Oyster HR Solutions Limited | Professional & scientific | 2007 |
| Oyster Innovations Limited | Professional & scientific | 2012 |
| Oysters Properties Ltd | Real estate | 2025 |
| OZ Global Ltd | Wholesale & retail | 2025 |
| OZ Trade Ltd | Wholesale & retail | 2025 |
| Ozanada Ltd | Hospitality | 2017 |
| Ozarikus Ltd | Wholesale & retail | 2025 |
| Ozdemir Consultancy and Planning Services Ltd | Professional & scientific | 2025 |
| Ozdes Ltd | Wholesale & retail | 2025 |
| Ozge Derin Ltd | Wholesale & retail | 2026 |
| Ozgursatilmisakademi Ltd | Wholesale & retail | 2025 |
| OZH Nucleo Limited | Wholesale & retail | 2025 |
| OZI Property Ltd | Real estate | 2021 |
| Ozindas Limited | Manufacturing | 2010 |
| Ozkerstore Ltd | Wholesale & retail | 2024 |
| Ozlemcek Ltd | Wholesale & retail | 2025 |
| Ozpolat Store Ltd | Wholesale & retail | 2024 |
| Ozum Ltd | Information & communication | 2006 |
| Ozuvan Ltd | Construction | 2023 |
| Ozvena Ltd | Wholesale & retail | 2024 |
| O’Briens Parcels Ltd | Transport & logistics | 2024 |
| O’Connell Bhatia Studio Ltd | Manufacturing | 2023 |
| P & a Land Developments Limited | Real estate | 2018 |
| P & a Land Ltd | Professional & scientific | 2012 |
| P & C Consultancy Limited | Administrative & support | 2009 |
| P & D Coins & Antiquities Limited | Wholesale & retail | 2010 |
| P & D Renovations Ltd | Manufacturing | 2019 |
| P & J Roofing and Landscaping Limited | Administrative & support | 2025 |
| P & J Transport Limited | Transport & logistics | 2017 |