| Notes Du Nord Norge AS | Wholesale & retail | 2019 |
| Nye Sentrum AS | Professional & scientific | 2011 |
| Nygårdsvingen SA | Real estate | 2012 |
| Nykirke Autosenter AS | Real estate | 1973 |
| Nystredet 4 Da | Real estate | 2006 |
| Nystredet AS | Real estate | 2021 |
| Nyvasket AS | Administrative & support | 2022 |
| Nyvik Holding AS | Real estate | 2007 |
| NÓN LÁ AS | Hospitality | 2024 |
| O Førlie AS | Wholesale & retail | 1931 |
| O&N Heen AS | Manufacturing | 2015 |
| O,Flynn AS | Professional & scientific | 2025 |
| O2 Invest AS | Financial services | 2005 |
| Odd Fellow Huset Berga AS | Real estate | 2026 |
| Odd Fellow Huset Berga SA | Real estate | 1954 |
| Ohela Invest AS | Financial services | 2005 |
| Ojf AS | Wholesale & retail | 1985 |
| Ok Trykk AS | Manufacturing | 1992 |
| Okan Eiendom Nuf | Real estate | 2021 |
| Ole Johan Lund-Johansen | Construction | 2008 |
| Ole Morten Furuseth AS | Construction | 2005 |
| Oliv Bar & Restaurant AS | Hospitality | 2019 |
| Oljerens AS | Wholesale & retail | 2025 |
| Oloy Holding AS | | 2019 |
| Omelune AS | Wholesale & retail | 2026 |
| Onsum Invest AS | Real estate | 1989 |
| Opera Østfold AS | Arts & recreation | 2019 |
| Opplev Haldenkanalen AS | Transport & logistics | 2022 |
| Optikon Eiendom AS | Real estate | 1981 |
| Ord Om Annet AS | Arts & recreation | 2019 |
| Organic Living AS | | 2023 |
| Oruds Prosjektservice AS | Professional & scientific | 2006 |
| Os Alle 11 AS | Real estate | 2013 |
| Os Allè 19B AS | Health & social care | 2014 |
| Os Allè Tannklinikk AS | Health & social care | 2014 |
| Os Allé 9 AS | Real estate | 2004 |
| Oscar Sæther AS | Real estate | 1936 |
| Oscars Gate 1 Utvikling AS | Real estate | 2026 |
| Osiso AS | | 2020 |
| Oskar L. Hansen AS | Construction | 1979 |
| Oskar L. Hansen Eiendom AS | Real estate | 1968 |
| Oslo Dagligvareeksperten AS | Wholesale & retail | 2023 |
| Osol Eiendom AS | Construction | 2016 |
| Osteo Consult AS | Health & social care | 2002 |
| Otkib Engineering AS | Professional & scientific | 2025 |
| Outlet Norway AS | | 2018 |
| P.0. Rørmyr AS | Construction | 2016 |
| P.M.C AS | | 2020 |
| P2 Bygg AS | Construction | 2018 |
| Pagel Industrimørtel AS | Wholesale & retail | 1978 |
| Palmi AS | | 2019 |
| Pam Eiendom Og Investering AS | Real estate | 2003 |
| Pangea Invest AS | Financial services | 2014 |
| Parabel Film AS | Information & communication | 1985 |
| Parfymeriet Anette AS | Wholesale & retail | 2008 |
| Parken Frisør Halden AS | Other services | 2021 |
| Pel AS | Professional & scientific | 2005 |
| Pellygata 64 Sarpsborg AS | Real estate | 2025 |
| Per Puck Eiendom AS | Real estate | 2004 |
| Pers Utemiljø AS | Construction | 2015 |
| Pesa AS | Professional & scientific | 2018 |
| Petersborg Invest AS | Manufacturing | 2010 |
| Peterson Eiendom Sarpsborg AS | Real estate | 2014 |
| Peterson Holding AS | Real estate | 2015 |
| Petter Mjølnerød AS | Real estate | 2018 |
| Pettersen Utemiljø AS | Administrative & support | 2020 |
| Phaljo Holding AS | | 2022 |
| Pianostredet Figurteater Da | Arts & recreation | 2018 |
| Pil AS | Manufacturing | 2023 |
| Pilo Konsult AS | Information & communication | 2019 |
| Pipe Eksperten AS | Construction | 2025 |
| Pitney Bowes Worldwide Inc. - Norway Branch Nuf | Professional & scientific | 2019 |
| Pizza Marco Polo Ans | Manufacturing | 1998 |
| Pizza'N På Brygga AS | Hospitality | 2021 |
| Plater & Kaffe Da | Wholesale & retail | 2000 |
| Plumeria AS | Real estate | 2019 |
| Poppærn Storkiosk Ans | | 1989 |
| Porsnes Eiendom AS | Real estate | 2011 |
| Porsnes Utvikling AS | Real estate | 2017 |
| Potor Eiendom AS | Construction | 2020 |
| Power Cable Consulting AS | Professional & scientific | 2013 |
| Powersupply AS | Real estate | 2014 |
| Preben Andersen AS | Construction | 2020 |
| Precis Norway Limited Nuf | Information & communication | 2008 |
| Preg Barnehager Halden AS | Education | 2022 |
| Prinktum AS | | 2026 |
| Pro Car Wash AS | Other services | 2018 |
| Proffhagen AS | Wholesale & retail | 2019 |
| Profittpartner Da | Professional & scientific | 2006 |
| Proflex Agentur AS | Real estate | 1991 |
| Proman Invest AS | Wholesale & retail | 2014 |
| Promptus AS | Information & communication | 2013 |
| Prospectum AS | Financial services | 2005 |
| Protoservice AS | Manufacturing | 2013 |
| Psi-Gruppen AS | Health & social care | 2011 |
| PV Holding AS | Real estate | 2005 |
| Pysjkompaniet AS | Wholesale & retail | 2026 |
| Python Data Da | Wholesale & retail | 1994 |
| Pytt I Panne Da | Manufacturing | 1997 |
| Påsan Invest AS | Manufacturing | 2024 |