| Oakpark Energy Ltd | Construction | 2024 |
| Oakpark Group Ltd | Administrative & support | 2026 |
| Oakridge Bookkeeping Limited | Professional & scientific | 2025 |
| Oakwood Renewables Limited | Construction | 2017 |
| Oapropertyinvestment Ltd | Real estate | 2022 |
| Oasis Property Services Ltd | Real estate | 2026 |
| OBA Tech Solutions Ltd. | Information & communication | 2010 |
| Occasion Creations Limited | Wholesale & retail | 2015 |
| ODD One OUT Construction Ltd | Construction | 2024 |
| Oeab Imaging Ltd | Health & social care | 2020 |
| OFF the Wagon Ltd | Hospitality | 2020 |
| OKE Ltd | Extraterritorial | 2025 |
| Old School Court Management (Buckingham) Limited | Households | 1997 |
| Old Town Hall Management Company Ltd | Real estate | 2012 |
| OLI Design Engineering Service Ltd | Professional & scientific | 2024 |
| Oliv-Harr Group Holdings Limited | Real estate | 2017 |
| Olive Grove Partners Ltd | Real estate | 2025 |
| Oliver Smith Contracting Limited | Construction | 2019 |
| Oly.B Ltd | Construction | 2023 |
| Omnia Europe Ltd | Administrative & support | 2015 |
| Omniscient Innovations Ltd | Information & communication | 2023 |
| ON Targett Events Ltd | Arts & recreation | 2011 |
| ON the Decks Group Limited | Education | 2025 |
| Onaya Limited | Health & social care | 2019 |
| Only Trade Vehicles Ltd | Wholesale & retail | 2025 |
| Onpoint Delivery Ltd | Transport & logistics | 2025 |
| Onsite Training UK Limited | Administrative & support | 2020 |
| Ontrack Supply Chain Limited | Wholesale & retail | 2019 |
| Open Air Foods Limited | Wholesale & retail | 2012 |
| Optec IT Solutions Ltd | Information & communication | 2016 |
| Opticworld Ltd | Wholesale & retail | 2015 |
| Orange Retail Ltd | Wholesale & retail | 2023 |
| Orchard Drive Residents Limited | Households | 2001 |
| Orchard Investment Holdings Limited | Financial services | 2026 |
| Ordriq Ltd | Information & communication | 2026 |
| Original Chilli Honey Ltd | Wholesale & retail | 2026 |
| Ortega-Llarena Consulting Limited | Professional & scientific | 2018 |
| Osberg Labs Ltd | Information & communication | 2025 |
| Oscar James Motor Sales Ltd | Wholesale & retail | 2022 |
| Ossfab Holdings Ltd | Financial services | 2024 |
| OV Consulting Limited | Professional & scientific | 2017 |
| Ovm-Group Co Limited | Transport & logistics | 2018 |
| OW Functions and Balls Ltd | Hospitality | 2024 |
| OX Locations Ltd | Water & waste | 2025 |
| Oxford Commercial Interiors Ltd | Construction | 2010 |
| Oxford Consulting Ltd | Professional & scientific | 2017 |
| Oxfordshire Linens Ltd | Administrative & support | 2024 |
| Oxfordshire Oak Frame Building's Ltd | Construction | 2017 |
| Oxley Green Management Company Limited | Households | 2013 |
| Oxman Carpentry Limited | Manufacturing | 2019 |
| Oxonhomes Limited | Real estate | 2015 |
| P & E Retail Limited | Wholesale & retail | 2013 |
| P & HB Limited | Water & waste | 2020 |
| P a Electrical and Controls Ltd | Construction | 2022 |
| P a P Limited | Professional & scientific | 1992 |
| P M Douglas Ltd | Real estate | 2022 |
| P&D Brown Consulting Ltd | Information & communication | 2024 |
| P.T.H. Stove Installations Ltd | Construction | 2011 |
| P.West Ltd | Information & communication | 2013 |
| Pace Motorsport Limited | Professional & scientific | 2011 |
| Padam Care Ltd | Health & social care | 2026 |
| Padbury Pre-School | Education | 2008 |
| Pado Limited | Professional & scientific | 2004 |
| PAI Consultancy Limited | Extraterritorial | 2013 |
| PAL2PREP Ltd | Information & communication | 2026 |
| Palina Ltd | Administrative & support | 2016 |
| Pangea Solutions Ltd | Information & communication | 2026 |
| Panzini Restaurants Limited | Hospitality | 2017 |
| Papa Figo 44 Limited | Financial services | 2024 |
| Papa LUI Pizza Ltd | Hospitality | 2019 |
| Paperklip Limited | Administrative & support | 2012 |
| Paperklip Office Services Limited | Professional & scientific | 2008 |
| Papoose Ltd | Information & communication | 2019 |
| Paragon Tool Hire Limited | Construction | 1993 |
| Parex Carpentry Ltd | Manufacturing | 2018 |
| Partnership Care Ltd | Health & social care | 2016 |
| Pasha Jewellery (Buckingham) Limited | Wholesale & retail | 2011 |
| Passion for Plants Limited | Wholesale & retail | 1998 |
| Passionate Helping Hands Limited | Administrative & support | 2022 |
| Paul Starkey Consulting Ltd | Professional & scientific | 2023 |
| Paul Templeman Professional Services Limited | Professional & scientific | 2015 |
| Pavilion Point Limited | Real estate | 2022 |
| Paxtonsgarage Ltd | Wholesale & retail | 2022 |
| PD Automotive Ltd | Wholesale & retail | 2024 |
| Peacocks Maintenance Services Ltd | Administrative & support | 2021 |
| Peak Building Consultants Ltd | Professional & scientific | 2019 |
| Peartree Engineering (Holdings) Ltd | Administrative & support | 2022 |
| Peartree Engineering Ltd | Manufacturing | 2022 |
| Pegasus Conservatories Limited | Construction | 1995 |
| Pelican Financial Planning Limited | Financial services | 2023 |
| Pelican Management Solutions Ltd | Administrative & support | 2020 |
| PEN Test Partners LLP | | 2010 |
| Pendragon Scientific Ltd | Manufacturing | 2009 |
| Pengard Limited | Administrative & support | 1972 |
| Penguin Leisure (Holdings) Limited | Financial services | 2019 |
| Penguin Leisure Construction Ltd | Construction | 2021 |
| Penguin Leisure Limited | Construction | 1994 |
| Penn Control Services Limited | Professional & scientific | 2009 |
| Penny Loveless Limited | Administrative & support | 2022 |
| People Artisans Ltd | Administrative & support | 2015 |