| Nordre Kullerød 10 AS | Real estate | 1996 |
| Nordre Kullerød 21A AS | Real estate | 2006 |
| Nordre Kullerød 21B AS | Real estate | 2017 |
| Nordskogen Da | Agriculture & fishing | 2017 |
| Nordtagg AS | Professional & scientific | 2022 |
| Norelko AS | Wholesale & retail | 2015 |
| Norenergi Gruppen AS | Professional & scientific | 2021 |
| Norfishco AS | Wholesale & retail | 2017 |
| Norges Bolig AS | Construction | 2023 |
| Norhybrid Renewables AS | Professional & scientific | 2020 |
| Normed AS | Health & social care | 2013 |
| Norner AS | Professional & scientific | 2012 |
| Norner Research AS | Professional & scientific | 2013 |
| Norrøna Holding AS | Wholesale & retail | 2005 |
| Norsk Førstehjelp Service AS | Education | 2019 |
| Norsk Investeringsgruppen AS | Construction | 2019 |
| Norsk Kompetanse Megling Da | Professional & scientific | 1998 |
| Norsk Områdesikring AS | Construction | 2011 |
| Norsk Områdesikring Itv AS | Construction | 2016 |
| Norsk Raffineringsverk Prosessrådgivning AS | Administrative & support | 1926 |
| Norsk Sprinklerteknikk AS | Construction | 2017 |
| Norsk Turboservice AS | Wholesale & retail | 1986 |
| Norskecodrive AS | Education | 2024 |
| North Capital Feeder CMR AS | Real estate | 2007 |
| North Capital Holding AS | Real estate | 2007 |
| Northowl Education Da | Information & communication | 2023 |
| Nortruck AS | Wholesale & retail | 1989 |
| Norvei Bil AS | Wholesale & retail | 2025 |
| Norwegian Briquetting AS | Financial services | 2005 |
| Norwegian Trustee Service on Behalf of Dominiok Da | Information & communication | 2018 |
| Norwegian Watch Company AS | Manufacturing | 2016 |
| Nova Invest AS | Financial services | 2005 |
| Novella Holding AS | Real estate | 2005 |
| NR Byggservice AS | Construction | 2026 |
| NR1 Trafikkskole Porsgrunn AS | Education | 2012 |
| NST 163001 AS | Construction | 2022 |
| Nucking Holding AS | | 2022 |
| Nustad Bolig AS | Real estate | 2019 |
| Nybnæring 2A AS | Real estate | 2024 |
| Nybnæring 2B AS | Real estate | 2024 |
| Nybnæring 2C AS | Real estate | 2024 |
| Nybuåsen Næringspark AS | Real estate | 2022 |
| Nybuåsen Tomteselskap AS | Real estate | 2019 |
| Nybuåsen Utbygging AS | Real estate | 2021 |
| Nye Down Town Helsekost AS | Wholesale & retail | 2024 |
| Nyen Holding AS | Financial services | 2018 |
| Nystrand Barnehage AS | Education | 2007 |
| Nystrand Holding AS | Professional & scientific | 2005 |
| Nystrand Invest AS | Hospitality | 2021 |
| Næringsareal AS | Real estate | 2011 |
| Nærum Bolig AS | Real estate | 2019 |
| Nøklegård Holding AS | | 2020 |
| O Kolle Holding AS | Construction | 2021 |
| O.M.L. Transport AS | Transport & logistics | 2024 |
| O.O.M.Holding AS | Real estate | 2008 |
| Oasen Fritid AS | Arts & recreation | 1993 |
| Obiter AS | Professional & scientific | 2018 |
| Odd Hanssen Herreekvipering AS | Wholesale & retail | 1964 |
| Oddbjørn Eiendom AS | Real estate | 1997 |
| Odero Eiendom AS | Real estate | 2018 |
| Odero Holding AS | | 2025 |
| Odhe Eiendom AS | Real estate | 2025 |
| Odit AS | Information & communication | 2020 |
| Oesk Holding AS | | 2023 |
| Ojm Eiendom AS | Real estate | 2018 |
| Olav Brekke AS | Other services | 2011 |
| Olavsberget Camping Og Badeplass AS | Hospitality | 2021 |
| Olavsberget Eiendom Ny AS | Real estate | 2025 |
| Olavsberget Holding AS | | 2023 |
| Olavsgaard AS | Real estate | 2021 |
| Olavsgate Utbygging AS | Real estate | 2017 |
| Olavsgt. 26 AS | Real estate | 2004 |
| Ole J Hagen Maskin AS | Construction | 2021 |
| Ole Jonny Madsen Maskinentreprenør AS | Construction | 1976 |
| Oljo-Invest AS | | 2021 |
| Oma Consulting AS | Information & communication | 2008 |
| Omea Gruppen AS | Financial services | 2022 |
| Omi Technologies AS | | 2026 |
| Omnileap AS | Professional & scientific | 2012 |
| Onebase AS | Real estate | 2007 |
| Onera Drift AS | Real estate | 2020 |
| Onera Eiendom AS | Real estate | 2015 |
| Onera Gruppen AS | Wholesale & retail | 2021 |
| Onezero Holding AS | Real estate | 2010 |
| Onyx 8 AS | Professional & scientific | 2026 |
| Onyx Ball AS | Information & communication | 2020 |
| Opal Audio Ans | | 1994 |
| Oppgruppen AS | Information & communication | 2012 |
| Oppkjøpsentralen AS | Transport & logistics | 1998 |
| Optiker Hogstad AS | Wholesale & retail | 2016 |
| Optimal Analyse AS | | 2020 |
| Optimal Consulting AS | Professional & scientific | 2026 |
| Opus-Prosjekt AS | Professional & scientific | 2017 |
| Orderx AS | Professional & scientific | 2016 |
| Orion AS | Other services | 1994 |
| Orod AS | Real estate | 2021 |
| Osebakken AS | Real estate | 2021 |
| Osebakken Motorservice AS | Wholesale & retail | 1997 |
| Osebro Antikvariat Da | Wholesale & retail | 2006 |
| Ostara Helse AS | Health & social care | 2023 |