| Optimus Auto Solutions Ltd | Wholesale & retail | 2023 |
| Optimus Business Services Limited | Professional & scientific | 2026 |
| Optimus Global Limited | Wholesale & retail | 2001 |
| Optimus Logistics L.T.D Ltd. | Wholesale & retail | 2025 |
| Optimus Private Clients Limited | Real estate | 2013 |
| Opulence Plus Ltd | Health & social care | 2022 |
| Opus 22 Ltd | Real estate | 2019 |
| Opus Wellbeing Limited | Health & social care | 2022 |
| ORA Fitness Prep and Wellness Limited | Arts & recreation | 2023 |
| ORA International Business Services Limited | Information & communication | 2013 |
| ORA Reseach Ltd | Professional & scientific | 2026 |
| Oracle ALT Beauty Ltd | Other services | 2022 |
| Orakul Safety Ltd. | Professional & scientific | 2025 |
| Oral Construction Services Ltd | Construction | 2024 |
| Orange Box North East C.I.C. | Wholesale & retail | 2016 |
| Orangezone London Ltd | Information & communication | 2014 |
| Orangutans Marketing Limited | Professional & scientific | 2016 |
| Oraprime Limited | Construction | 2007 |
| Oraprime Orthodontics Limited | Health & social care | 2007 |
| ORB Electrics (North East) Limited | Construction | 2005 |
| Orbequirus Limited | Real estate | 2022 |
| Orbit Capture Limited | Professional & scientific | 2026 |
| Orbit Marketing Group Limited | Professional & scientific | 2026 |
| Orbit Recruitment Group Ltd | Administrative & support | 2019 |
| Orbital FX Ltd | Information & communication | 2024 |
| ORC Sadberge Ltd | Construction | 2026 |
| Orca 11 Ltd | Administrative & support | 2022 |
| Orca LGS Solutions Limited | Construction | 2012 |
| Orchard Consulting & Development Ltd | Professional & scientific | 2023 |
| Orchard Country Apartments Limited | Real estate | 2010 |
| Orchard Mews (Eaglescliffe) Management Company Limited | Households | 2005 |
| Orchard Place Residents Association Limited | Households | 1994 |
| Orchard Street Service Co Ltd | Administrative & support | 2009 |
| Ordafy Limited | Wholesale & retail | 2024 |
| Order of Bards Ovates & Druids CIC | Other services | 2023 |
| Ordermatic Limited | Professional & scientific | 2023 |
| Ordinal Interiors Limited | Construction | 2017 |
| Organix Consulting Limited | Professional & scientific | 2019 |
| Orient Property Group North East Ltd | Real estate | 2026 |
| Oriental Garden Monkseaton Limited | Hospitality | 2013 |
| Origin Greens Ltd | Agriculture & fishing | 2025 |
| Origin Integrity Management Ltd | Professional & scientific | 2011 |
| Original Galleries Ltd | Other services | 2020 |
| Original Gallery Ltd | Arts & recreation | 2019 |
| Original Lishman's Limited | Other services | 2019 |
| Orion Consulting Services Limited | Information & communication | 2018 |
| Orion Digital Limited | Information & communication | 2016 |
| Orion Online Ltd | Wholesale & retail | 2026 |
| Orion Property Services Ltd | Households | 2020 |
| Orion Technology Services Ltd | Information & communication | 2023 |
| Orix Accountants Ltd | Professional & scientific | 2016 |
| Oriyii Holdings Ltd | Financial services | 2026 |
| Ormston Drylining Ltd | Construction | 2022 |
| Orraman Leather Ltd | Manufacturing | 2024 |
| Orthodontics Ltd | Health & social care | 2025 |
| Ortus Economic Research Limited | Professional & scientific | 2017 |
| Orvex Global Ltd | Wholesale & retail | 2026 |
| Orvis Properties Ltd | Real estate | 2022 |
| OSA FAM Investments Limited | Financial services | 2018 |
| Osas Afro Foods Ltd | Wholesale & retail | 2023 |
| Osborne Directors Limited | Professional & scientific | 2003 |
| Osborne House (Jesmond) Management Limited | Households | 1999 |
| Osborne Leisure Limited | Hospitality | 2026 |
| Osborne Medical Company Limited | Health & social care | 2004 |
| Osborne Real Estate Limited | Real estate | 2019 |
| Osborne Residential Limited | Real estate | 2023 |
| Osborne Road (131) Limited | Households | 1984 |
| Osborne Secretaries Limited | Professional & scientific | 2003 |
| OSC REU Ltd | Real estate | 2025 |
| OSE European Ltd | Transport & logistics | 2018 |
| Osemuahu Company Limited | Health & social care | 2013 |
| Osiris Press Limited | Information & communication | 2024 |
| Osiris Systems Limited | Information & communication | 2023 |
| Osis Capital Ltd | Professional & scientific | 2026 |
| Oskap (Commercial) Limited | Real estate | 2004 |
| Oskap Limited | Real estate | 1998 |
| Oskari Limited | Professional & scientific | 2012 |
| Osli Properties Ltd | Real estate | 2025 |
| Otterburn Holdings Limited | Professional & scientific | 2008 |
| Otterburn Investments Limited | Real estate | 2003 |
| Otthon Ltd | Real estate | 2025 |
| OTTOMAN1299 Ltd | Hospitality | 2026 |
| OU Books Limited | Professional & scientific | 2011 |
| Oubas LLP | | 2011 |
| Oubas One Ltd | Construction | 2020 |
| Oubinov Cleaning Services Limited | Administrative & support | 2020 |
| Oubinov Ltd | Wholesale & retail | 2015 |
| OUD Lovers Ltd | Transport & logistics | 2020 |
| OUR Friends in the North 2026 Production Limited | Arts & recreation | 2026 |
| OUR Local Tour Ltd | Administrative & support | 2022 |
| Ouseburn Beauty Limited | Other services | 2019 |
| Ouseburn Bike Works Ltd | Wholesale & retail | 2022 |
| Ouseburn Coffee Company Ltd | Manufacturing | 2011 |
| Ouseburn Community Centre Trading CIC | Administrative & support | 2026 |
| Ouseburn Consulting Ltd | Professional & scientific | 2026 |
| Ouseburn Developments Limited | Construction | 2016 |
| Ouseburn Farm Charity Limited | Education | 2011 |
| Ouseburn Learning Trust | Education | 2014 |
| Ouseburn Property Developments Limited | Construction | 2018 |
| Ouseburn Trust | Real estate | 1996 |