| Nye Møller Invest AS | | 2026 |
| Nye Salong Hage AS | Other services | 1996 |
| Nye Strømsø Holding AS | Hospitality | 2022 |
| Nygaard Investering AS | | 2022 |
| Nygård Benestad Da | Agriculture & fishing | 2002 |
| Nyhetsanalyse AS | Information & communication | 2026 |
| Nylænder Invest AS | | 2026 |
| Nynas AS | Manufacturing | 1991 |
| Nysnee AS | Professional & scientific | 2012 |
| Nystua AS | Professional & scientific | 2012 |
| Nyttige Idéer AS | Professional & scientific | 2018 |
| NZ Holding AS | | 2026 |
| Nordanger A/S | Real estate | 1976 |
| Norløff Holding A/S | Real estate | 1987 |
| Nästegård AS | Real estate | 2020 |
| Næringsbygg II AS | Real estate | 2011 |
| Næringsbygg III AS | Real estate | 2017 |
| Næringsbygg Invest AS | Real estate | 2018 |
| Næslund Invest AS | Wholesale & retail | 2005 |
| Næslund Metal Trading AS | Wholesale & retail | 1985 |
| Nævra AS | Professional & scientific | 2006 |
| Nøste Eiendom AS | Real estate | 2010 |
| Nøste Hovedgård AS | Real estate | 2025 |
| Nøste HR AS | Real estate | 2022 |
| Nøste Invest AS | Professional & scientific | 2013 |
| Nøste Utleie AS | Real estate | 2015 |
| Nøsted AS | Real estate | 2006 |
| Nøsted Brygge Bolig AS | Real estate | 1993 |
| Nøsted Eiendom AS | Real estate | 2005 |
| Nøsted Marina AS | Real estate | 2009 |
| O'Learys Restaurants Drammen AS | Hospitality | 2021 |
| O. Strand Invest AS | | 2025 |
| Oa Bakke Invest AS | Professional & scientific | 2015 |
| Oa Kraglund AS | | 2019 |
| Obas Invest AS | Hospitality | 2020 |
| Obas Øst AS | Construction | 2001 |
| Obm Invest AS | Construction | 2025 |
| Obst Grafisk AS | Professional & scientific | 2017 |
| OCEAN1 AS | Professional & scientific | 2005 |
| Oceansaver AS | Manufacturing | 2003 |
| Ocnet AS | Information & communication | 2022 |
| Octopus Investments AS | | 1987 |
| Odd Fellowgården AS | Real estate | 1949 |
| Odd Jensen Trafikkskole AS | Education | 1994 |
| Oddvar Olsen & Co AS | Wholesale & retail | 2006 |
| Odelsbygg 3-SCHJØTTELVIK AS | Real estate | 2018 |
| Odysée Cater Ans | Hospitality | 1999 |
| Oe Bygg & Invest AS | Real estate | 2013 |
| Oem-Automatic AS | Wholesale & retail | 1981 |
| Oes Filtbygg AS | Financial services | 2021 |
| Off the Lip AS | Wholesale & retail | 2013 |
| Offentlig Data AS | Information & communication | 2026 |
| Offset AS | | 2024 |
| Ohm Elektro AS | Construction | 2025 |
| Ohs Holding AS | Professional & scientific | 2005 |
| Oikos Invest AS | | 2026 |
| Oikos Kaffe AS | Manufacturing | 2024 |
| Oisann Invest AS | | 2021 |
| Ojj Invest AS | | 2025 |
| Ok Anleggsservice AS | Construction | 2002 |
| Ok Kjemi Drammen AS | Manufacturing | 1994 |
| Okc Invest AS | | 2021 |
| Okse Holding AS | | 2024 |
| Ola SL Consult AS | Professional & scientific | 2020 |
| Olajens Denim AS | Professional & scientific | 2014 |
| Old Gold 47 AS | Wholesale & retail | 2025 |
| Old Man Games Da | Information & communication | 2025 |
| Ole 2 Eiendom AS | Real estate | 2025 |
| Ole 2 Invest AS | | 2025 |
| Ole a Fevang AS | Financial services | 2005 |
| Ole CHR Hagen Ans | Transport & logistics | 1985 |
| Ole K Og Bjarne a Aaserud Ans | Agriculture & fishing | 1974 |
| Ole M Invest AS | | 2022 |
| Ole Selvig Eiendom AS | Real estate | 1970 |
| Ole-Anders Enger AS | Real estate | 2025 |
| Ole-Mikael Sørsdahl AS | | 2021 |
| Oles Invest & Design AS | Construction | 2012 |
| Oline Invest AS | Real estate | 2004 |
| Oljafondet AS | Financial services | 2018 |
| Olores Holding AS | Construction | 2010 |
| Olsen IT AS | Financial services | 2014 |
| Olsens Enke Drammen AS | Wholesale & retail | 2018 |
| Olympus Trening AS | Education | 2013 |
| Omatemi AS | Real estate | 2022 |
| Omatemi Holding AS | | 2026 |
| Ombe Accounting AS | Professional & scientific | 2019 |
| Omega Bedriftsrådgivning AS | Professional & scientific | 1988 |
| Omholttunet AS | Real estate | 2026 |
| Omica AS | Administrative & support | 2026 |
| Omlof Holding AS | | 2023 |
| Omni Nordic AS | Wholesale & retail | 2019 |
| Omnia Sounds AS | Information & communication | 2020 |
| Omnibo Nord AS | Real estate | 2003 |
| Omnibo Vest AS | Real estate | 2014 |
| Omniscient AS | Professional & scientific | 2014 |
| Omsira AS | Health & social care | 2025 |
| Omsorg Konsult AS | Health & social care | 2021 |
| On Edge Sports Da | Wholesale & retail | 2011 |
| On Property AS | Information & communication | 2012 |
| One-Shot Norge AS | Wholesale & retail | 2008 |