| Offset Energy Management Limited | Professional & scientific | 2012 |
| Offshore Blue Limited | Financial services | 2019 |
| Offshore Blue Property Limited | Real estate | 2025 |
| Offsite Construction Detailing Ltd | Construction | 2018 |
| OG Italiano Ltd | Hospitality | 2023 |
| OG Professional Services Ltd | Education | 2026 |
| OGD Engineering Ltd | Manufacturing | 2021 |
| Ogden-Swift Consulting Limited | Professional & scientific | 2017 |
| OGGY1 Limited | Construction | 2025 |
| Ogis Logistics Limited | Transport & logistics | 2020 |
| Ogkils & Supery Ltd | Wholesale & retail | 2024 |
| OGS Cooling Limited | Administrative & support | 2013 |
| Ohama Ltd | Extraterritorial | 2024 |
| Ohana Hobby Workshop Ltd | Wholesale & retail | 2025 |
| OHD 1 Limited | Construction | 2010 |
| Ohitslailak Ltd | Other services | 2022 |
| Ohms Electrical Contracting Ltd | Other services | 2016 |
| Ohmspace Ltd | Professional & scientific | 2020 |
| OIL of Joy Limited | Health & social care | 2025 |
| OIL Spill Response (Capping) Limited | Professional & scientific | 2012 |
| OIL Spill Response Limited | Administrative & support | 1984 |
| Oishii Soton Limited | Hospitality | 2024 |
| OJB Smith Group Holding Ltd | Financial services | 2026 |
| OJS Ultrasound Solutions Ltd | Health & social care | 2019 |
| OJW GAS Services Limited | Construction | 2020 |
| OK Homes Ltd | Households | 2020 |
| OK, TRY This NOW! Ltd | Professional & scientific | 2024 |
| OK4U2 Limited | Health & social care | 2022 |
| Okey Holdings Ltd | Financial services | 2021 |
| Oktic Ltd | Transport & logistics | 2016 |
| Oktoberfest South Ltd | Arts & recreation | 2017 |
| Okwi Distribution Ltd | Wholesale & retail | 2024 |
| OLA Agnes Ltd | Wholesale & retail | 2019 |
| Olani Cleaning Services Ltd | Administrative & support | 2025 |
| Olari Construction Ltd | Construction | 2025 |
| Old Comical Ltd | Hospitality | 2024 |
| Old Common (Property) Limited | Real estate | 2018 |
| Old Farmhouse PUB Ltd | Hospitality | 2019 |
| Old Forge Projects Limited | Real estate | 2019 |
| Old Oak Carpentry Limited | Construction | 2014 |
| Old Redbridge Flats Limited | Real estate | 2003 |
| Old School Mews (Seaford) Resident Management Company Limited | Households | 2004 |
| Old School Place Residents Limited | Households | 2015 |
| Old ST Labs Ltd | Information & communication | 2012 |
| Old Tannery (Downton) Limited | Households | 2003 |
| Old Town Property Holdings Limited | Financial services | 2025 |
| Olden Commercials & Fabrications Ltd | Manufacturing | 2022 |
| Oldtimer Services Limited | Transport & logistics | 2016 |
| Olga Transport Ltd | Transport & logistics | 2022 |
| Olgatone Coffee Limited | Wholesale & retail | 2019 |
| Olgun Digital & E-Commerce Ltd | Information & communication | 2019 |
| Oli&G Ltd | Transport & logistics | 2019 |
| Oliphant Developments Limited | Construction | 1986 |
| Olivbell Limited | Professional & scientific | 2009 |
| Olive Branch Group Limited | Real estate | 2018 |
| Olive Electronics Ltd | Professional & scientific | 2006 |
| Olive IT Ltd | Information & communication | 2025 |
| Olive Tree Children's Home | Professional & scientific | 2009 |
| Olive Tree Construction Ltd | Construction | 2021 |
| Oliver and Harvey PUB Co Ltd | Hospitality | 2025 |
| Oliver Morgan Ltd | Wholesale & retail | 2025 |
| Oliver Property Development Ltd | Real estate | 2024 |
| Oliver Solutions Ltd | Information & communication | 2017 |
| Oliver Wagg Limited | Professional & scientific | 2019 |
| Oliverwhyte.Og Global Limited | Health & social care | 2023 |
| Olivia Roberts Limited | Construction | 2024 |
| OLLI43 Ltd | Information & communication | 2014 |
| Ollie Malone's Hair and Holistic Beauty Ltd | Other services | 2025 |
| Ollivers Limited | Real estate | 2017 |
| Oltwa Limited | Public administration | 2021 |
| Oluna Aesthetics Ltd | Other services | 2026 |
| Oluwafemi Medical Limited | Health & social care | 2022 |
| Olympus Consulting Ltd | Information & communication | 2023 |
| Olynex Ltd | Information & communication | 2025 |
| OM Haan Limited | Hospitality | 2023 |
| OM SAI GOA Cuisine Limited | Hospitality | 2020 |
| Omar 3 Ltd | Hospitality | 2022 |
| Omar Distinct Ltd | Other services | 2018 |
| Omar Estates Limited | Real estate | 2020 |
| Omart Ltd | Wholesale & retail | 2025 |
| Omati Limited | Transport & logistics | 2021 |
| Omcmedia Ltd | Professional & scientific | 2023 |
| Omega Commerce Limited | Wholesale & retail | 2023 |
| Omega RE Ltd | Real estate | 2020 |
| Omeireh Limited | Health & social care | 2023 |
| OMF Partition Services Limited | Construction | 2020 |
| OMH Enterprises Ltd | Administrative & support | 2017 |
| Omkaar Limited | Wholesale & retail | 2006 |
| Omni Commerce Limited | Professional & scientific | 2011 |
| Omnia House Limited | Real estate | 2022 |
| Omnia Living Solutions Limited | Health & social care | 2023 |
| Omnichest Limited | Wholesale & retail | 2026 |
| Omnicomm, Ltd | Information & communication | 2009 |
| Omnilux Limited | Information & communication | 2021 |
| Omnio Technologies Ltd | Information & communication | 2001 |
| Omnipack Limited | Wholesale & retail | 2016 |
| Omnipathway Limited | Wholesale & retail | 2023 |
| Omnipol Accounting Ltd | Professional & scientific | 2010 |
| Omnipotent Digital Ltd | Professional & scientific | 2026 |
| Omniprescent Ltd | Wholesale & retail | 2026 |