| Nxtg Holding AS | | 2025 |
| Nybø Eiendom AS | Real estate | 2007 |
| Nye Flattum Tannlegesenter AS | Health & social care | 2026 |
| Nye Mat AS | | 2021 |
| Næring AS | Real estate | 2023 |
| O.R.Rolund AS | Agriculture & fishing | 2024 |
| Odd Martin Midsem | Wholesale & retail | 2007 |
| Odd Palerud AS | Manufacturing | 1995 |
| Oddvar Thoen AS | Construction | 1995 |
| Odel Rådgivning AS | Professional & scientific | 2016 |
| Odelskraft AS | Professional & scientific | 2024 |
| Odelskraft Consulting AS | Professional & scientific | 2009 |
| Oet 612 Holding AS | | 2023 |
| Office Center Eiendom AS | Real estate | 2006 |
| Oksana Renhold AS | Administrative & support | 2020 |
| Olav Holding AS | | 2017 |
| Olav Tryterud Studio AS | Other services | 2018 |
| Olonana Holding AS | Arts & recreation | 2008 |
| Omegaklinikken Hønefoss AS | Health & social care | 2024 |
| Omhu Barn, Ungdom Og Familie AS | Health & social care | 2020 |
| Omhu Helse Og Omsorg AS | Health & social care | 2021 |
| Omhu Holding AS | Health & social care | 2016 |
| Omsorgsbygg Hønefoss AS | Real estate | 2020 |
| Onshus Invest AS | | 2024 |
| Onwrd AS | | 2025 |
| Oochi Studios AS | Other services | 2025 |
| Opdahl Bygg & Rehab AS | Construction | 2021 |
| Opdahl Holding AS | Real estate | 2018 |
| Opero Drift AS | Wholesale & retail | 2023 |
| Oph Holding AS | | 2022 |
| Oppen Holding AS | Real estate | 2022 |
| Oppen Sikt AS | Real estate | 2022 |
| Opperud Eiendom AS | Real estate | 1997 |
| Opperud Holding AS | Real estate | 2005 |
| Oppløpssiden AS | Professional & scientific | 2026 |
| Opprettselskap AS | Hospitality | 2021 |
| Or Holding AS | | 2005 |
| Oscar Knutsen AS | Wholesale & retail | 2026 |
| Osloveien 23 AS | Real estate | 1989 |
| Osloveien 23 II AS | Real estate | 2019 |
| Osloveien 34B AS | Real estate | 2022 |
| Ossum Legetjeneste AS | Health & social care | 2005 |
| Ottar Engebretsen Holding AS | Real estate | 2005 |
| Owrens Gate 9 AS | Real estate | 2017 |
| Ozzy AS | Real estate | 2017 |
| Olsen Import ANS | Wholesale & retail | 1988 |
| P60 Drift AS | Manufacturing | 1997 |
| P60 Holding AS | Real estate | 2021 |
| Pace Athletic Wear AS | Wholesale & retail | 2023 |
| Pada Holding AS | Professional & scientific | 2022 |
| Pafe Holding AS | Real estate | 2019 |
| Pal Byggservice AS | Construction | 2018 |
| Pal Entreprenør AS | Construction | 2021 |
| Parkering AS | Real estate | 2023 |
| Parkogidrett AS | Health & social care | 2024 |
| Partio AS | Professional & scientific | 2022 |
| Pasmos AS | Construction | 2008 |
| Patica Holding AS | | 2021 |
| Paulsrud Eiendom AS | Real estate | 2020 |
| Pedersen Maskindrift AS | Construction | 2018 |
| Peer Invest AS | Professional & scientific | 2019 |
| Per Bye AS | Construction | 2006 |
| Per Halgrim Piltingsrud AS | Professional & scientific | 2013 |
| Per Holm Holding AS | Real estate | 2017 |
| Per J Gundersen AS | Wholesale & retail | 1984 |
| Pera Invest AS | Financial services | 2014 |
| Perform AS | Wholesale & retail | 2017 |
| Permobakken AS | Real estate | 2017 |
| Peter Nordahl AS | Wholesale & retail | 2017 |
| Petershagen AS | Real estate | 2020 |
| PG Smykker Da | Wholesale & retail | 2015 |
| Pga Eiendom AS | Construction | 1986 |
| PGB AS | | 2020 |
| PGB International AS | Real estate | 2010 |
| Phonefiks AS | Other services | 2018 |
| Pia Dalevold AS | Wholesale & retail | 1998 |
| Pia Holding AS | | 2019 |
| Pinball Norge AS | Wholesale & retail | 2021 |
| Pinehill AS | Information & communication | 2016 |
| Pirol Invest AS | Financial services | 2013 |
| Plastomer Norway AS | Wholesale & retail | 2018 |
| PMJ Holding AS | | 2023 |
| PMK Holding AS | | 2023 |
| Port Øst AS | Construction | 2018 |
| Positiv Support AS | Professional & scientific | 2019 |
| Pottit Bua AS | Hospitality | 2023 |
| Preanalyse AS | Education | 2022 |
| Prestmarken Bil AS | Wholesale & retail | 2004 |
| Prestmarken Bilservice AS | Other services | 2018 |
| Prestmarken Holding AS | Wholesale & retail | 1997 |
| Pretty Pitchy Da | Professional & scientific | 2025 |
| Privatmegleren Hønefoss AS | Real estate | 2023 |
| Pro Auto Service AS | Other services | 2019 |
| Pro-Holding AS | Real estate | 2005 |
| Probicus AS | Professional & scientific | 1990 |
| Proffsenteret AS | Wholesale & retail | 2008 |
| Proffsenteret Eiendom AS | Real estate | 2022 |
| Profil Holding AS | Real estate | 2005 |
| Profil Montering AS | Construction | 2003 |
| Prosidius AS | Professional & scientific | 2013 |