| ONE2CREATE Limited | Information & communication | 2003 |
| Oneglow Ltd | Wholesale & retail | 2024 |
| Ongrade Limited | Wholesale & retail | 2009 |
| Onitronics Ltd | Wholesale & retail | 2020 |
| Onle Holdings Limited | Financial services | 2020 |
| Online PC Support Limited | Information & communication | 2005 |
| Online Youth Manager Ltd | Information & communication | 2012 |
| Only Hounds Ltd | Other services | 2023 |
| Onsite Services DW Limited | Manufacturing | 2010 |
| Onvupa Enterprise Limited | Hospitality | 2025 |
| Onward Healthcare Limited | Health & social care | 2013 |
| Onyx Arch & Co. Ltd | Construction | 2022 |
| Onyx Groundworks and Civil Engineering Ltd | Construction | 2022 |
| Oona&Isabella Transport Ltd | Transport & logistics | 2023 |
| Oorja Power Systems Ltd | Information & communication | 2024 |
| OP Properties Ltd | Real estate | 2022 |
| Open Conservation Technology Ltd | Professional & scientific | 2019 |
| Open Road Hats Ltd | Professional & scientific | 2021 |
| Opoho and Old Goaled Security Company Limited | Administrative & support | 2024 |
| Opoho Limited | Other services | 2012 |
| Optimum Computer Maintenance Limited | Information & communication | 2002 |
| Orbis Business Intelligence Limited | Professional & scientific | 2009 |
| Orchard View Property Developments Ltd | Construction | 2003 |
| Organice by Paida Ltd | Extraterritorial | 2020 |
| Organists Charitable Trust | Health & social care | 1935 |
| ORH Associates Limited | Information & communication | 2026 |
| Oriental Source Trading Ltd | Wholesale & retail | 2018 |
| Ormonde Consulting Ltd. | Professional & scientific | 2016 |
| Oryxcom Ltd | Construction | 2023 |
| OS BMS Limited | Construction | 2022 |
| Osborne Hobbies Ltd | Wholesale & retail | 2026 |
| Osemka Ltd | Transport & logistics | 2023 |
| OSM Holdings Ltd | Financial services | 2020 |
| Ossature Property Group Limited | Real estate | 2023 |
| Other Life Limited | Administrative & support | 2022 |
| Others Limited | Professional & scientific | 2003 |
| Otif Global Ltd | Wholesale & retail | 2025 |
| Ottaway Engineering Limited | Manufacturing | 1968 |
| Otterbourne Care Limited | Health & social care | 2021 |
| OUR Harmony Hub CIC | Public administration | 2025 |
| OUT of Office Supplies Ltd | Wholesale & retail | 2025 |
| Outreach FM Limited | Information & communication | 2009 |
| Outreach Radio Limited | Information & communication | 2021 |
| Oxford International Education & Travel Limited | Administrative & support | 1991 |
| Oxford International Education 1 Limited | Financial services | 2014 |
| Oxford International Education 2 Limited | Financial services | 2014 |
| Oxford International Education 3 Limited | Financial services | 2014 |
| Oxford International Education Group Ltd | Financial services | 1993 |
| Oxford International Education Group Services Limited | Administrative & support | 2017 |
| Oxford International School Limited | Education | 2016 |
| Oxford International Worldwide Educational Services Limited | Education | 2022 |
| Oxford Tutorial College Ltd. | Education | 1994 |
| Oxlease Residents Limited | Households | 2016 |
| Ozhd Ltd | Wholesale & retail | 2023 |
| P & E Jones Ltd | Financial services | 2024 |
| P & M (Packing) Limited | Transport & logistics | 2006 |
| P & S Builders Ltd | Construction | 2015 |
| P B Hospitality Consultants Ltd | Hospitality | 2022 |
| P D Scammell Limited | Construction | 1996 |
| P E P I Consultancy Limited | Health & social care | 2022 |
| P Lambert Limited | Real estate | 2012 |
| P P Catering & Events Limited | Hospitality | 2013 |
| P R Moody Ltd | Wholesale & retail | 2012 |
| P Watson Project Services Limited | Construction | 2016 |
| P&A Property REN Limited | Construction | 2024 |
| P&M NPD Ltd | Wholesale & retail | 2025 |
| P&O Professional (Southern) Limited | Construction | 2025 |
| P&P Business Limited | Professional & scientific | 2013 |
| P&R Plastering and Rendering Ltd | Construction | 2025 |
| P-M Surveying Limited | Professional & scientific | 2022 |
| P. Kingcott Limited | Manufacturing | 1982 |
| P.H Electrical & Home Improvements Limited | Construction | 2018 |
| P.J.Drew(Engravers)Limited | Manufacturing | 1965 |
| P.S. Plumbing and Heating Limited | Construction | 2000 |
| PAB Supply Chain Solutions Ltd | Professional & scientific | 2023 |
| Paddington Holdings Limited | Financial services | 2017 |
| Paddington Plastering & DRY Lining Limited | Construction | 1989 |
| Paddington Properties Limited | Real estate | 2017 |
| Paddington Screeding Limited | Construction | 2017 |
| Page Management Limited | Real estate | 2020 |
| Palladian Court Management Company Limited | Households | 2005 |
| Palmer Lighting Ltd | Arts & recreation | 2022 |
| Pampered Piggies CIC | Agriculture & fishing | 2026 |
| Pandun Property Partners Limited | Real estate | 2024 |
| Panoptic Cloud Ltd | Information & communication | 2026 |
| Pantheon Leasing Limited | Administrative & support | 2008 |
| Paper Engine Ltd | Information & communication | 2011 |
| Parcel Right Limited | Transport & logistics | 2024 |
| Park Car Wash Ltd | Other services | 2017 |
| Park Crescent Limited | Households | 2006 |
| Park Imaging Limited | Administrative & support | 2019 |
| PARKING4CRUISES Ltd | Administrative & support | 2011 |
| PARKING4FLIGHTS Limited | Extraterritorial | 2013 |
| Parkway 1632 Ltd | Real estate | 2023 |
| Parkway Car Sales Ltd | Wholesale & retail | 2003 |
| Parkway Tdmp Holding Limited | Financial services | 2022 |
| Parkwood Document Solutions Limited | Information & communication | 2007 |
| Part a Ltd | Wholesale & retail | 2026 |
| Partnerwise Advisory Ltd | Professional & scientific | 2025 |
| Partridge Vehicle Leasing Limited | Wholesale & retail | 2023 |