| Offshore Procurement & Engineering Services Ltd | Wholesale & retail | 2011 |
| OG Traders Limited | Wholesale & retail | 2025 |
| Oghe Services Limited | Administrative & support | 2009 |
| Oghohen Limited | Health & social care | 2010 |
| Ohanaeze Ndigbo UK Limited | Other services | 2014 |
| OIA Media Ltd | Information & communication | 2025 |
| OIL & GAS Insights Ltd | Wholesale & retail | 2022 |
| OJ Sing Sing Limited | Other services | 2017 |
| Ojuolape Limited | Health & social care | 2014 |
| Okiki Promotion Limited | Wholesale & retail | 2019 |
| Okrema UK Ltd | Construction | 2016 |
| Okxpress Ltd | Wholesale & retail | 2025 |
| Oladar Consulting Limited | Financial services | 2016 |
| Oladsco Electrical Consultant Serice Limited | Manufacturing | 2025 |
| Olakennygrace Limited | Health & social care | 2012 |
| Olamijo Ltd | Real estate | 2026 |
| Olayinka Care Limited | Health & social care | 2019 |
| Olbish Ventures Limited | Health & social care | 2021 |
| Old Monea Trans Ltd | Transport & logistics | 2012 |
| Oleh Tkach Limited | Construction | 2025 |
| OLI Cars Ltd | Wholesale & retail | 2024 |
| OLI Energy Ltd | Construction | 2024 |
| Olimp Delivery Ltd | Transport & logistics | 2020 |
| Oline Bedding Ltd | Wholesale & retail | 2016 |
| Olion Bookkeeping Ltd | Professional & scientific | 2023 |
| Olion Limited | Professional & scientific | 2020 |
| Oliram Ltd | Construction | 2022 |
| Olive Well Coffee & Bistro Ltd | Hospitality | 2023 |
| Olive Well Ltd | Wholesale & retail | 2019 |
| Olivers Drywall Finishing Ltd | Construction | 2019 |
| Olives Social Care Services Ltd | Health & social care | 2025 |
| Olivet Homecare Limited | Health & social care | 2022 |
| Olivia Branch Childcare Limited | Health & social care | 2023 |
| Olivstan Ltd | Administrative & support | 2026 |
| Oltenia Expert Limited | Construction | 2017 |
| Oltenia RO Ltd | Wholesale & retail | 2017 |
| Olumide a Odubawo Limited | Health & social care | 2022 |
| Oluwasogo Limited | Real estate | 2025 |
| Olykay Ltd | Construction | 2025 |
| OM Aesthetic Yoga Ltd | Education | 2015 |
| Omaroad Contractors Ltd | Construction | 2024 |
| Omega Fire Ministries | Other services | 2012 |
| Omega Nigerian Takeaway Limited | Hospitality | 2025 |
| Omega Plastering Ltd | Construction | 2014 |
| Omegadrywall Ltd | Construction | 2017 |
| Omego (UK) Limited | Health & social care | 2008 |
| Omies Empire Limited | Wholesale & retail | 2025 |
| Omniserve Global Ltd | Professional & scientific | 2026 |
| Omon Ltd | Health & social care | 2024 |
| Omonigee & Co Ltd | Health & social care | 2015 |
| Omons Tasty Ltd | Hospitality | 2025 |
| Omorufi Property Services Limited | Construction | 2024 |
| Omrag Ltd | Wholesale & retail | 2019 |
| Omsn Limited | Real estate | 2026 |
| OMT Metalworks Limited | Manufacturing | 2025 |
| Onboard Tech Solutions Limited | Information & communication | 2026 |
| Ondego Ltd | Transport & logistics | 2025 |
| Ondo Ekimogun Youth UK Ltd | Other services | 2023 |
| One BAG Ltd | Health & social care | 2025 |
| One Caal Rubbish Removal Limited | Water & waste | 2024 |
| One Mail Ltd | Transport & logistics | 2019 |
| One PAW at a Time Project Ltd | Other services | 2025 |
| One Step Investment Ltd | Real estate | 2022 |
| One Stop Cloud Ltd | Information & communication | 2012 |
| One Stop Electronics Ltd | Wholesale & retail | 2024 |
| One Touch Construction Ltd | Construction | 2016 |
| One Wise Property Ltd | Real estate | 2020 |
| One World Venture UK Limited | Transport & logistics | 2025 |
| Onebitz Ltd | Information & communication | 2026 |
| Onecornerstore Ltd | Wholesale & retail | 2025 |
| Onehot Ltd | Wholesale & retail | 2024 |
| Onel Construction Ltd | Construction | 2022 |
| Onel Salon & Boutique Ltd | Wholesale & retail | 2024 |
| Onereference Ltd | Information & communication | 2025 |
| Onestep Consult Ltd Limited | Administrative & support | 2019 |
| Ongo Coffee Ltd | Hospitality | 2025 |
| ONI Plumbing & Heating Ltd | Construction | 2022 |
| Online Blinds 2 YOU Limited | Wholesale & retail | 2020 |
| Online Truck and Trailer Parts Limited | Wholesale & retail | 2015 |
| Onlineretailplus Limited | Wholesale & retail | 2026 |
| ONO Belle Global Ltd | Other services | 2014 |
| Onoh Care Ltd | Health & social care | 2013 |
| Onpoint Drainage Solutions Ltd | Administrative & support | 2025 |
| ONPOINT247 Limited | Health & social care | 2015 |
| Ontime Taxi Services Ltd | Transport & logistics | 2018 |
| Onusha Ltd | Wholesale & retail | 2024 |
| Onyilings Limited | Health & social care | 2014 |
| Onyx Trade Ltd | Wholesale & retail | 2026 |
| OO and Triple J UK Limited | Households | 2022 |
| Oopharma Ltd | Health & social care | 2025 |
| Oorja Limited | Information & communication | 2011 |
| OP7PROF Ltd | Construction | 2022 |
| Opal Linen Store Ltd | Wholesale & retail | 2024 |
| Open Cleaning Ltd | Administrative & support | 2024 |
| Open Core Tech Limited | Information & communication | 2026 |
| Open Day Drywall Ltd | Construction | 2022 |
| Open Gates International Ltd | Health & social care | 2026 |
| Open Heavens Limited | Health & social care | 2008 |
| Open Spaces Consultancy Ltd | Administrative & support | 2025 |
| Opex Trade Group Ltd | Wholesale & retail | 2025 |