| Oriel House Exeter Management Co. Limited | Administrative & support | 1983 |
| Oriels Exeter Limited | Hospitality | 2025 |
| Origin Cleanse Limited | Wholesale & retail | 2025 |
| Origin Land Ltd | Construction | 2020 |
| Original Style Holdings Limited | Professional & scientific | 2010 |
| Original Style Limited | Manufacturing | 1995 |
| Orionesque Limited | Information & communication | 2004 |
| Orlana Homes Ltd | Real estate | 2025 |
| Orpheus Corporation Holdings Limited | Financial services | 2005 |
| Ortus SW Limited | Construction | 2012 |
| OSBORNE74 Limited | Professional & scientific | 2017 |
| Oscar 21 Ltd | Hospitality | 2026 |
| Oscar Catering Ltd | Hospitality | 2023 |
| Oscar Exeter Ltd | Other services | 2023 |
| Osiko Holdings Ltd | Financial services | 2025 |
| Osiko Properties Ltd | Real estate | 2025 |
| Osman-Price Property Investments Limited | Real estate | 2023 |
| Osprey Development ( Applemead ) Ltd | Construction | 2017 |
| Osprey Development (March) Limited | Construction | 2017 |
| Osteo and Physio Newton Abbot Ltd | Health & social care | 2023 |
| Osteo and Physio Ottery Ltd | Other services | 2019 |
| Ostler Developments Limited | Construction | 2024 |
| Ostler Inn Limited | Hospitality | 2023 |
| OTP Building Services Limited | Extraterritorial | 2000 |
| Otter Angling Limited | Wholesale & retail | 2016 |
| Otter House Limited | Information & communication | 1991 |
| Otter Motors Ltd | Wholesale & retail | 2015 |
| Otterbourne Court Management Co. Limited | Households | 1974 |
| Otters Reach Management Company Limited | Households | 2025 |
| Otterton Mill (Devon) Ltd | Wholesale & retail | 2015 |
| Ottervale Haulage Limited | Manufacturing | 2000 |
| Ouch Mouse Ltd | Financial services | 2024 |
| OUR Echo Ltd | Information & communication | 2024 |
| OUR Exeter CIC | Information & communication | 2024 |
| OUR Homes Group Ltd | Extraterritorial | 2022 |
| OUR Rainwater Limited | Professional & scientific | 2021 |
| Ousted Ltd | Wholesale & retail | 2023 |
| OUT of the Box Innovations Limited | Information & communication | 2015 |
| OUT There Living Limited | Wholesale & retail | 2021 |
| OUT There Together CIC | Professional & scientific | 2025 |
| Outback Properties Ltd | Construction | 2016 |
| Outdoor Living South West Limited | Construction | 2025 |
| Outlawed Productions Ltd | Information & communication | 2023 |
| Outline Beauty Ltd | Health & social care | 2025 |
| Outreach Southwest C.I.C. | Education | 2024 |
| Outsourced Medical Secretary Solutions UK Ltd | Administrative & support | 2023 |
| Ouzaria Limited | Hospitality | 1996 |
| Ovation Catering Solutions Ltd | Hospitality | 2017 |
| Overair Ltd | Information & communication | 2016 |
| Overall Construction Limited | Construction | 1992 |
| Overland Court Management Company Limited | Households | 2001 |
| Overmatch Defence Systems Ltd | Wholesale & retail | 2026 |
| Overnight Solutions Ltd | Transport & logistics | 2022 |
| Oversight Services Ltd | Administrative & support | 2025 |
| Owen and Company Building Surveyors Ltd | Professional & scientific | 2018 |
| Owen Arts Limited | Professional & scientific | 2001 |
| Oxbio Ltd | Professional & scientific | 2023 |
| Oxbridge Tutor Group Ltd | Education | 2022 |
| Oxford Sports Education Limited | Education | 2018 |
| Oxford Trade Frames Limited | Administrative & support | 1997 |
| Oxfordshire Heritage Windows Limited | Construction | 2016 |
| Oxi-Tech Solutions Limited | Water & waste | 2017 |
| Oxley River Capital Ltd | Financial services | 2021 |
| Oxton Estates & Holdings Ltd. | Real estate | 2017 |
| Oxton House Limited | Households | 1984 |
| Oxygen Conservation Holdings 1 Limited | Real estate | 2022 |
| Oxygen Conservation Holdings 1B Limited | Real estate | 2023 |
| Oxygen Conservation Limited | Real estate | 2021 |
| Oxygen Conservation Portfolio 1 Limited | Financial services | 2025 |
| Oxygen House Group Limited | Financial services | 2012 |
| Oxygen House Limited | Professional & scientific | 2008 |
| OZ Windows Limited | Construction | 2011 |
| Ozbek Properties (SW) Ltd | Households | 2020 |
| P & a Properties (SW) Limited | Construction | 2005 |
| P & B Contractors Limited | Construction | 2021 |
| P & D Developments (South West) Limited | Construction | 2013 |
| P & G Contractors (SW) Ltd | Construction | 2024 |
| P & G Developments (SW) Ltd | Construction | 2024 |
| P & G Property Developments Ltd | Real estate | 2016 |
| P & G White Property Ltd | Real estate | 2021 |
| P & J Chown Plumbing & Heating Limited | Construction | 2021 |
| P a C Management Company (Exeter) Limited | Real estate | 2016 |
| P Deare Carpentry & Joinery Ltd | Construction | 2014 |
| P Deare Crane Hire Ltd | Construction | 2025 |
| P Deare Holdings Limited | Financial services | 2023 |
| P F Electrical (SW) Ltd | Construction | 2022 |
| P F Electrical South West Limited | Construction | 2021 |
| P H Bricklaying Limited | Construction | 2024 |
| P J Davidson Developments Ltd | Financial services | 2003 |
| P J Davidson Holdings Ltd. | Professional & scientific | 2009 |
| P J Davidson Sporting Ltd | Administrative & support | 2009 |
| P J. Rose Haulage Contractors Limited | Transport & logistics | 2003 |
| P K Optics Limited | Wholesale & retail | 2025 |
| P O Developments Limited | Other services | 2019 |
| P R Nautica Yacht Management Services Limited | Manufacturing | 2014 |
| P Vennelle Limited | Agriculture & fishing | 2011 |
| P&B Properties (SW) Ltd | Real estate | 2024 |
| P&G HR Ltd | Administrative & support | 2024 |
| P.J.F. Electrical Services Ltd | Construction | 2024 |
| P1 Investment Services Limited | Financial services | 2015 |