| Olives Afro- Caribbean Shop Ltd | Manufacturing | 2026 |
| Olivibra UK Limited | Wholesale & retail | 2012 |
| Oliwia Service Ltd | Transport & logistics | 2020 |
| Ollintel Limited | Information & communication | 2015 |
| Olly Lloyd Stunts Ltd | Information & communication | 2022 |
| OM Live Breathe Yoga & Sound Therapy CIC | Health & social care | 2025 |
| Omanba Foods Limited | Wholesale & retail | 2025 |
| Omega (Cheltenham) Limited | Real estate | 1985 |
| Omega Housing Limited | Households | 2010 |
| Omega Housing Services Ltd | Education | 2021 |
| Omega Results Limited | Information & communication | 2004 |
| Omega UX Group Ltd | Information & communication | 2025 |
| Omiga Technology Limited | Information & communication | 2000 |
| OMM Solutions Ltd | Other services | 2015 |
| Omnicard Limited | Information & communication | 2025 |
| Omobaba Properties Limited | Real estate | 2026 |
| OMS Dental Limited | Health & social care | 2023 |
| ON Call Maintenance (Glos) Ltd | Administrative & support | 2024 |
| ON Demand Print & Design Limited | Manufacturing | 2010 |
| ON Fire Coaching Ltd | Professional & scientific | 2017 |
| ON the Table Community Ltd | Hospitality | 2019 |
| ON3 Rentals Ltd | Wholesale & retail | 2010 |
| Onatura Ltd | Administrative & support | 2024 |
| Onbrand Workwear Limited | Wholesale & retail | 2024 |
| One Car Trade Limited | Wholesale & retail | 2024 |
| One Church | Other services | 2009 |
| One Community Gloucester | Hospitality | 2009 |
| One Islam Ltd | Other services | 2025 |
| One Service Portal Limited | Information & communication | 2008 |
| One Stop Plumbing & Heating Services Ltd | Construction | 2018 |
| ONE7 Developments Limited | Construction | 2025 |
| Onepie Ltd | Wholesale & retail | 2021 |
| Oneteam Ltd | Administrative & support | 2013 |
| Ongo Market Ltd | Information & communication | 2026 |
| Onion Properties Limited | Real estate | 2016 |
| Onion Property Lettings Ltd | Real estate | 2020 |
| Onsung Trading Ltd | Wholesale & retail | 2023 |
| Ontrac Consultancy Services Ltd | Construction | 2022 |
| Onward Digital Ltd | Professional & scientific | 2017 |
| Onward Holdings Group Ltd | Financial services | 2025 |
| Onyx Workgear Limited | Administrative & support | 2013 |
| Opaleye and Middlefell Limited | Health & social care | 2010 |
| Opalux Group (FDS) Limited | Construction | 2026 |
| Opalux Group Limited | Construction | 2024 |
| Opalux Investment Group Limited | Real estate | 2024 |
| Opasta One Ltd | Wholesale & retail | 2025 |
| OPD Auto Services Ltd | Wholesale & retail | 2025 |
| Opearl Limited | Real estate | 2022 |
| Open House Cheltenham Ltd | Real estate | 2020 |
| Open Imaging Ltd | Health & social care | 2025 |
| Open Plan Specialists Limited | Construction | 2023 |
| Openarms Housing Ltd | Health & social care | 2022 |
| Openview Doors & Windows Limited | Construction | 2020 |
| Operandi Magic Limited | Arts & recreation | 2014 |
| Operation Consultancy Limited | Professional & scientific | 2025 |
| Operatum Consulting Ltd | Professional & scientific | 2025 |
| Ophthalmic Technology Ltd | Professional & scientific | 2014 |
| OPO Bakery Ltd | Manufacturing | 2023 |
| Oppulant Ltd | Wholesale & retail | 2011 |
| Optamus Limited | Construction | 2018 |
| Optilearn Ltd | Education | 2021 |
| Optima Staffing Solutions Limited | Administrative & support | 2016 |
| Optimal Chiropractic & Health Limited | Health & social care | 2024 |
| Optimal Facilities Management Ltd. | Professional & scientific | 2015 |
| Optimas OE Solutions Ltd | Wholesale & retail | 2015 |
| Optimising IT Holdings Ltd | Financial services | 2020 |
| Optimistik Glazing Ltd | Manufacturing | 2024 |
| Optimum Carpentry Solutions Ltd | Construction | 2019 |
| Optisan Ltd | Professional & scientific | 2020 |
| Opyx Digital Ltd | Information & communication | 2025 |
| OQS Orthos Quality Services Ltd | Construction | 2020 |
| Oral Store Ltd | Wholesale & retail | 2025 |
| Oramo Holdings Ltd | Financial services | 2021 |
| Oramo Lettings Ltd | Real estate | 2021 |
| Orange Juice Rentals Limited | Information & communication | 2023 |
| Orange Moon Luxury Spirits Limited | Wholesale & retail | 2024 |
| Orange One Finlab Ltd | Education | 2026 |
| Orbexia Ltd | Information & communication | 2024 |
| Orbit Bloodstock Limited | Agriculture & fishing | 2019 |
| Orchard Barns Apperley Ltd | Households | 2023 |
| Orchard Close (Bredon) Management Company Limited | Households | 2011 |
| Orchard Court (Cheltenham) Limited | Households | 2003 |
| Orchard Grove Management Limited | Administrative & support | 1990 |
| Orchard Guardians C.I.C. | Agriculture & fishing | 2000 |
| Orchard Homes (Glos) Ltd | Construction | 2019 |
| Orchard Leigh Bonchurch Ltd | Extraterritorial | 2018 |
| Orchard Quay Management Limited | Real estate | 2004 |
| Orchards Farm Shop Ltd | Wholesale & retail | 2024 |
| ORD Group Limited | Financial services | 2024 |
| Orient Eden Ltd | Wholesale & retail | 2026 |
| Origin Advisory Ltd | Professional & scientific | 2026 |
| Origin Decorative Limited | Wholesale & retail | 2018 |
| Origin Living Ltd | Education | 2025 |
| Original Accountancy Limited | Professional & scientific | 2016 |
| Original Spin Ltd | Information & communication | 2024 |
| Orion Estate Management Limited | Households | 2024 |
| Orivaya Limited | Information & communication | 2026 |
| Orizaba Distribution Ltd | Wholesale & retail | 2003 |
| Orizaba Group Ltd | Financial services | 2017 |
| Orizaba Packaging Ltd | Real estate | 2021 |