| ON the Button Property Services Ltd | Construction | 2024 |
| ON1CLUB Ltd. | Wholesale & retail | 2020 |
| ON1CLUB Midlands Ltd | Wholesale & retail | 2024 |
| Oncotherapy Resources Limited | Health & social care | 2012 |
| Oncredible Group Limited | Wholesale & retail | 2023 |
| One Berkeley Limited | Real estate | 2024 |
| One Big Bite Walsall Limited | Hospitality | 2019 |
| One Express (Midlands) Limited | Transport & logistics | 2024 |
| One Key Management Ltd | Real estate | 2025 |
| One Key Property Services Limited | Real estate | 2019 |
| One Life Financial Services Limited | Financial services | 2013 |
| One Love Community Music and Arts CIC | Arts & recreation | 2017 |
| One More Ltd | Hospitality | 2026 |
| One Place Support Centre Ltd | Professional & scientific | 2024 |
| One Source Accountants Ltd | Professional & scientific | 2022 |
| One Stop Car Wash & Tyre Centre Ltd | Wholesale & retail | 2025 |
| One Stop Community Stores Limited | Wholesale & retail | 1924 |
| One Stop Convenience Stores Limited | Wholesale & retail | 1990 |
| One Stop Garage Walsall Ltd | Wholesale & retail | 2018 |
| One Stop Retail Midlands Ltd | Wholesale & retail | 2021 |
| One Stop Stores Limited | Construction | 1990 |
| One Stop Stores Trustee Services Limited | Professional & scientific | 1990 |
| One Touch Quality Kare Limited | Health & social care | 2010 |
| One World Care Limited | Health & social care | 2023 |
| ONE7 Logistics Group Ltd | Transport & logistics | 2026 |
| Online Frontier Ltd | Wholesale & retail | 2014 |
| Online Marketing Maven Ltd | Extraterritorial | 2015 |
| Online Poundshop Limited | Wholesale & retail | 2014 |
| Online TAG Limited | Professional & scientific | 2025 |
| Only Quality Meat Ltd | Wholesale & retail | 2026 |
| Onsitearmor Ltd | Wholesale & retail | 2025 |
| ONU Deals Limited | Wholesale & retail | 2025 |
| Onward Commercial Ltd | Administrative & support | 2020 |
| Onward Hire Ltd | Wholesale & retail | 2010 |
| Opal Transport Equipment Limited | Professional & scientific | 1976 |
| Opatech Photography Ltd | Professional & scientific | 2026 |
| Open Door Lettings and Property Management Limited | Real estate | 2008 |
| Open Door Sales Ltd | Real estate | 2017 |
| Open Infra Ltd | Construction | 2021 |
| Open Interiors Limited | Construction | 2003 |
| Open Lens Media CIC | Administrative & support | 2013 |
| Open Lens Productions Ltd. | Information & communication | 2014 |
| Open Space Nurseries Limited | Education | 2007 |
| Opening ALL Rounder Group Limited | Financial services | 2026 |
| Openthorpe Engineering Limited | Manufacturing | 1981 |
| Operator SRF Limited | Transport & logistics | 2019 |
| Operatr Technologies Limited | Information & communication | 2026 |
| Opes Q Limited | Information & communication | 2026 |
| Opesq Consultancy Limited | Information & communication | 2026 |
| Opins Solutions Ltd | Real estate | 2021 |
| Oprd Limited | Extraterritorial | 2013 |
| Optical and Hearing Centre Ltd | Health & social care | 2009 |
| Optical Confederation Limited | Professional & scientific | 2010 |
| Optical Lens Solutions Limited | Manufacturing | 2006 |
| Optimum Haulage Ltd | Transport & logistics | 2025 |
| Optimum Mechanical & Electrical Installations Ltd | Construction | 2025 |
| Optimum Property Investment Limited | Real estate | 2023 |
| Optimus Enterprises Ltd | Professional & scientific | 2026 |
| Optimus Transport Ltd | Transport & logistics | 2017 |
| Optispa Ltd | Administrative & support | 2017 |
| Optom Academy Limited | Education | 2017 |
| Opulence Group Global Ltd | Real estate | 2024 |
| Opulence H B a Ltd | Other services | 2025 |
| Opulence Windows Ltd | Construction | 2023 |
| Opulent Mortgages Ltd | Financial services | 2025 |
| Oqab Solutions Limited | Professional & scientific | 2025 |
| Oracleproductionz Limited | Administrative & support | 2022 |
| Oraco Dental Ltd | Health & social care | 2006 |
| Oraco Ltd | Health & social care | 2009 |
| Oram (Lysways Street) Limited | Households | 1998 |
| Orange Electrical Contractors Ltd | Construction | 2017 |
| Orange Electrical Projects Limited | Construction | 2022 |
| Orange Fire & Security Ltd | Administrative & support | 2023 |
| Orange Flamingo Limited | Administrative & support | 2017 |
| Orange Holdings ( Midlands ) Ltd | Administrative & support | 2019 |
| Orange Residential Limited | Real estate | 2021 |
| ORB Print Limited | Manufacturing | 2010 |
| Orbit Botanical Ltd | Wholesale & retail | 2025 |
| Orbit Motor Service & Tyres Ltd | Wholesale & retail | 2020 |
| Orbital 10 Ltd | Information & communication | 2021 |
| Orbixio Ltd | Information & communication | 2025 |
| Orca One Limited | Professional & scientific | 2022 |
| Orchard Hills Bakery Limited | Wholesale & retail | 2021 |
| Orchid Cleaners Ltd | Administrative & support | 2020 |
| Orchid Medical Care Services Ltd | Administrative & support | 2017 |
| Orchids Healthcare Limited | Health & social care | 2022 |
| Ordinary Minded Ltd | Professional & scientific | 2023 |
| Ordinary Minds Ltd | Health & social care | 2021 |
| Oregano Pizza Ltd | Hospitality | 2025 |
| Oren Services Ltd | Construction | 2024 |
| Orenda Insight Limited | Administrative & support | 2017 |
| Orevastyle Limited | Wholesale & retail | 2025 |
| Organic Village Eclectic Foods Limited | Hospitality | 2015 |
| Organik Design Limited | Information & communication | 2008 |
| Orgreen Naturals Ltd | Wholesale & retail | 2018 |
| Orient Autos Limited | Wholesale & retail | 2026 |
| Oriental Express GAO Ltd | Hospitality | 2021 |
| Oriental Express Kitchen Ltd | Hospitality | 2026 |
| Oriental Express Walsall Ltd | Hospitality | 2024 |
| Oriental Express Walshall Ltd | Hospitality | 2023 |