| Oceanmind Limited | Information & communication | 2017 |
| Octeca Ltd | Professional & scientific | 2017 |
| Ofjb Ltd | Information & communication | 2023 |
| Ogoor-Maxdrive Limited | Transport & logistics | 2013 |
| Okero Design Ltd | Information & communication | 2023 |
| Okie Dokie Wash Limited | Wholesale & retail | 2025 |
| Olir-H Limited | Health & social care | 2021 |
| Oliwia Trans Limited | Transport & logistics | 2018 |
| Omai Nails Beauty Ltd | Other services | 2024 |
| Omed KRD Ltd | Wholesale & retail | 2025 |
| Omgrh Ltd | Financial services | 2023 |
| Omgrps Ltd | Financial services | 2023 |
| Omlrh (ES) Ltd | Financial services | 2023 |
| Omlrps (ES) Ltd | Financial services | 2023 |
| One for the Ajes Limited | Real estate | 2026 |
| One Motion Auto Services Ltd | Wholesale & retail | 2014 |
| One Motion Freight Services UK Ltd | Transport & logistics | 2022 |
| One Motion Fulfillment Ltd | Transport & logistics | 2022 |
| One Motion Group Limited | Financial services | 2018 |
| One Motion Logistics (ES) Ltd | Transport & logistics | 2023 |
| One Motion Logistics (IE) Ltd | Transport & logistics | 2023 |
| One Motion Logistics Ltd | Transport & logistics | 2014 |
| One Motion Transport UK Ltd | Transport & logistics | 2022 |
| One Oak React Ltd | Construction | 2025 |
| Ononna Didcot Limited | Hospitality | 2023 |
| Ononox Limited | Professional & scientific | 2017 |
| Open Cosmos Ltd. | Professional & scientific | 2015 |
| Open Retail Limited | Information & communication | 2021 |
| Openworldlab Ltd | Information & communication | 2026 |
| OPS 4 Hire Ltd | Administrative & support | 2023 |
| Optiworks Solutions Limited | Professional & scientific | 2024 |
| Opuz Ltd | Information & communication | 2022 |
| Orange Tree Technologies Limited | Manufacturing | 2001 |
| Orchard Mews (Chilton) Management Company Limited | Households | 2019 |
| Orchard ST Ltd. | Professional & scientific | 2011 |
| Organised Grime Ltd | Water & waste | 2022 |
| Origin Enterprises Digital Limited | Agriculture & fishing | 2013 |
| Orlando Homes Ltd | Real estate | 2021 |
| Orrock Holdings Limited | Financial services | 2019 |
| Orzechowski Construction Ltd | Construction | 2020 |
| OTS Distribution Limited | Wholesale & retail | 2026 |
| Otsdigipod Limited | Wholesale & retail | 2025 |
| Ounsworth Limited | Information & communication | 2016 |
| OUR Islamic Gift Store Limited | Wholesale & retail | 2022 |
| Outfox BIO Limited | Professional & scientific | 2021 |
| Outthinkr Ltd | Professional & scientific | 2026 |
| OVS Global Ltd | Information & communication | 2015 |
| Owlscote Management Co Limited | Households | 2017 |
| Ownmade Studios Ltd | Construction | 2020 |
| OX11 Consulting Limited | Professional & scientific | 2010 |
| Oxford Biopigments Ltd | Manufacturing | 2021 |
| Oxford City Angels CIC | Other services | 2022 |
| Oxford City Flooring Limited | Construction | 2010 |
| Oxford Composite Wood Ltd | Wholesale & retail | 2019 |
| Oxford Cosmetics Limited | Manufacturing | 2026 |
| Oxford Creators CIC | Education | 2022 |
| Oxford Decorating Limited | Construction | 2003 |
| Oxford Dreams Ltd | Households | 2026 |
| Oxford Dynamics Limited | Professional & scientific | 2019 |
| Oxford GI Limited | Information & communication | 2025 |
| Oxford Pet Whisperers Ltd | Other services | 2018 |
| Oxford Ritual Capital Ltd | Wholesale & retail | 2024 |
| Oxford Sign Studio Limited | Manufacturing | 2026 |
| Oxford Space Systems Limited | Professional & scientific | 2013 |
| Oxford Sports Medicine Limited | Health & social care | 2020 |
| Oxford Stoves Ltd | Construction | 2022 |
| Oxford Tea Parties Ltd | Other services | 2017 |
| Oxford West END Properties Ltd | Real estate | 2025 |
| Oxford Windows and Doors Limited | Construction | 2018 |
| Oxfordexcellence Inspections Ltd | Information & communication | 2020 |
| Oxfords Info Ltd | Information & communication | 2026 |
| Oxfordshire Drama Wardrobe Collection | Education | 2002 |
| Oxfordshire Family Support Network | Health & social care | 2011 |
| Oxfordshire Home Care Ltd | Health & social care | 2021 |
| Oxfordshire Music School Ltd | Education | 2022 |
| Oxfordshire Pet Services Limited | Other services | 2014 |
| Oxfordshire Properties - Lettings and Developments Ltd | Real estate | 2019 |
| Oxfordshire Property Ltd | Real estate | 2024 |
| Oxfordshire Remedials Limited | Construction | 2025 |
| Oxfordshire Renovations Ltd | Construction | 2021 |
| Oxfordshire Sign Company Ltd | Manufacturing | 2017 |
| Oxfordshire Weight Loss Clinic Ltd | Health & social care | 2025 |
| Oxfordshire Wellbeing Limited | Other services | 2025 |
| Oxiway Limited | Information & communication | 2012 |
| Oxlabs Limited | Manufacturing | 2020 |
| Oxon Impex Limited | Wholesale & retail | 2013 |
| Oxon Removals Ltd | Transport & logistics | 2020 |
| Oxonian Developments Limited | Construction | 2009 |
| Oxroc Ltd | Professional & scientific | 2022 |
| Oxware Technologies Ltd | Information & communication | 2021 |
| Oxygenomics Ltd | Administrative & support | 2017 |
| Oxytocin-Learning Ltd | Professional & scientific | 2025 |
| Oyster Bay Property Ltd | Real estate | 2023 |
| P 3 I Ltd | Wholesale & retail | 2003 |
| P Cohen Consultants Limited | Professional & scientific | 2014 |
| P J S Designs Limited | Manufacturing | 2010 |
| Packaging Products Direct Limited | Wholesale & retail | 1999 |
| PAE Rail Ltd | Wholesale & retail | 2023 |
| Papermill Enterprises Ltd | Wholesale & retail | 2021 |
| PAR Overseas Educational and Professional Consultancy Ltd | Professional & scientific | 2021 |