| Odpoledne Limited | Administrative & support | 2009 |
| Odyssey Activewear Ltd | Wholesale & retail | 2021 |
| OE Operations Ltd | Professional & scientific | 2025 |
| Oello Limited | Information & communication | 2019 |
| Oetker Investments Ltd | Construction | 2024 |
| OF the North Ltd. | Administrative & support | 2013 |
| OFF the Canvas Events Ltd | Arts & recreation | 2025 |
| OFF the Ground Pole Dance Ltd | Arts & recreation | 2025 |
| OFF the Rails Boutique Limited | Wholesale & retail | 2018 |
| OFF the Rails Enterprises Limited | Professional & scientific | 2024 |
| Offan Stellarrealm Cocoanee Limited | Wholesale & retail | 2025 |
| Offbeat Beauty Collective Limited | Other services | 2023 |
| Offbeat Folk Film Festival CIC | Information & communication | 2025 |
| Offertower Limited | Financial services | 1990 |
| Office & Commercial Relocation Limited | Transport & logistics | 2001 |
| Office Car Park Limited | Administrative & support | 2022 |
| Office Compliance Management Limited | Professional & scientific | 2014 |
| Office Friendly Limited | Professional & scientific | 1999 |
| Office Hunt Limited | Real estate | 2018 |
| Office Matters Limited | Administrative & support | 2016 |
| Office OUT Ltd | Wholesale & retail | 2020 |
| Official Sports Tutu’S Limited | Manufacturing | 2024 |
| Offstage Limited | Hospitality | 1989 |
| Offthecanvas CIC | Education | 2025 |
| Ofnc (Over 60’S) New Revived Group Sheffield Branch Limited | Other services | 2026 |
| OGC Energy Ltd | Professional & scientific | 2015 |
| Ogden Properties Ltd | Real estate | 2020 |
| Ogden Trade Limited | Wholesale & retail | 2026 |
| OGE Ventures Ltd | Health & social care | 2023 |
| Ogle-Timson Ltd | Wholesale & retail | 2025 |
| OGS Electrical Ltd | Construction | 2009 |
| Ogymber Ltd | Information & communication | 2026 |
| OH Assist Finance Limited | Administrative & support | 2015 |
| OH Assist Intermediate Limited | Administrative & support | 2015 |
| OH Assist Limited | Professional & scientific | 2015 |
| OH My Days Shop Limited | Wholesale & retail | 2021 |
| Ohaa Food Ltd | Hospitality | 2026 |
| Ohla Ltd | Administrative & support | 2018 |
| Ohms Electrical Ltd | Manufacturing | 2025 |
| Ohso Creative Ltd | Information & communication | 2011 |
| OIG Power Ltd. | Manufacturing | 2019 |
| Oisoi Gate Crasher City Food Market Limited | Wholesale & retail | 2017 |
| OJ & KS Properties Ltd | Real estate | 2025 |
| OJ Coaching Ltd | Information & communication | 2020 |
| OJ Construction Limited | Construction | 2019 |
| OJP Brickwork Ltd | Construction | 2025 |
| OK Mushroom Ltd | Education | 2025 |
| OK Tasty Food Ltd | Hospitality | 2023 |
| Okay James Ltd | Information & communication | 2017 |
| Okemb Services Limited | Construction | 2025 |
| Oker Farm Limited | Hospitality | 2023 |
| Oker Retreats Limited | Hospitality | 2022 |
| OKO Lashes & Brows Ltd | Other services | 2020 |
| OLA Consultants Ltd | Professional & scientific | 2022 |
| OLA Services Ltd | Administrative & support | 2023 |
| Ola's Cleaning Services Ltd | Administrative & support | 2025 |
| Olaad Cynosure Limited | Wholesale & retail | 2020 |
| Olashow Property Limited | Real estate | 2026 |
| Olberon Limited | Professional & scientific | 2005 |
| Olcato Commercial Services Limited | Administrative & support | 2023 |
| Olcom Ltd | Professional & scientific | 2024 |
| Old Big Head Limited | Arts & recreation | 2014 |
| Old BUT Gold Vintage Ltd | Wholesale & retail | 2018 |
| Old Chilly Pictures Ltd | Information & communication | 2023 |
| Old Dairy Properties Limited | Real estate | 2006 |
| Old Flavor Resturant Limited | Hospitality | 2025 |
| Old Fulwood Estates Limited | Real estate | 2018 |
| Old Hall Accountancy Ltd | Professional & scientific | 2016 |
| Old Hall Brightholmlee Limited | Construction | 2015 |
| Old Harrow Grenoside Ltd | Hospitality | 2026 |
| Old HAY Gardens (Dore) Limited | Households | 1973 |
| Old MAN Strength Ltd | Information & communication | 2018 |
| Old PIN Diner Ltd | Hospitality | 2018 |
| Old School Charity (Trustees) | Arts & recreation | 2012 |
| Old Way Two Limited | Hospitality | 2021 |
| Oldcotes Car Boot and Sunday Market Limited | Administrative & support | 2004 |
| Oldfield & SON Engineering & Fabrication Limited | Professional & scientific | 2008 |
| Oldfield Estate Management Ltd | Real estate | 2020 |
| Oldfield Masonry Limited | Construction | 2023 |
| Oldfield Rental Ltd | Real estate | 2026 |
| Oldham Agencies Limited | Wholesale & retail | 2000 |
| Oldham Engineering Limited | Manufacturing | 1993 |
| Oldways Building & Construction Ltd | Construction | 2025 |
| Oledo Consulting Ltd | Wholesale & retail | 2025 |
| Oleo Design Ltd | Professional & scientific | 2019 |
| Oleo Ecology Ltd | Professional & scientific | 2021 |
| Oleo Property Management Ltd | Real estate | 2023 |
| Olga & Asquith Products Ltd | Manufacturing | 2019 |
| OLI Mumby Creative Limited | Professional & scientific | 2016 |
| Oliander Ltd | Professional & scientific | 2021 |
| Olinda Gardens Maintenance Company Ltd | Real estate | 2022 |
| Olisia Ltd | Information & communication | 2016 |
| Olive & Sage Catering Limited | Hospitality | 2025 |
| Olive - Grove (Greenhill ) Limited | Wholesale & retail | 2024 |
| Olive Consultancy Limited | Education | 2023 |
| Olive Garden Ltd | Hospitality | 2026 |
| Olive Green Productions Ltd | Information & communication | 2022 |
| Olive Home Living Ltd | Households | 2025 |
| Olive House Restaurant Ltd | Hospitality | 2023 |
| Olive Nabili Limited | Hospitality | 2017 |