| Ose Holding AS | Real estate | 2008 |
| Ose Invest AS | | 2023 |
| Osiris Eiendom Holding AS | Real estate | 2015 |
| Oskar Pedersen AS | Wholesale & retail | 1925 |
| Osl Hub AS | Financial services | 2012 |
| Oslo Avenue AS | Real estate | 2019 |
| Oslo Tea Company AS | Wholesale & retail | 2022 |
| Oslofjorden Tomteutvikling AS | Real estate | 2000 |
| Osmund B. AS | Real estate | 2006 |
| Osmund Stray AS | Financial services | 2005 |
| Oso Capital AS | Professional & scientific | 2025 |
| Ososo Invest Da | Financial services | 2007 |
| Osp Holding AS | Information & communication | 2016 |
| Osylte AS | Real estate | 2018 |
| Ot Dental AS | Financial services | 2013 |
| Ot Holding AS | | 2005 |
| Otera Infra AS | Construction | 2010 |
| Otium Information Technology AS | Wholesale & retail | 1996 |
| Otm Eiendom AS | Real estate | 2005 |
| Otra Eiendom AS | Real estate | 2021 |
| Otra Holding AS | Real estate | 2013 |
| Otra Terrasse AS | | 2005 |
| Otratunet AS | Real estate | 2007 |
| Otrobanda AS | Information & communication | 2011 |
| Otros Holding AS | Real estate | 2021 |
| Ottosen AS | Manufacturing | 2018 |
| Our Family Software AS | Information & communication | 2019 |
| Outlet Cars AS | Wholesale & retail | 2023 |
| Outstanding Promotion AS | Professional & scientific | 2024 |
| Ovani AS | | 2016 |
| Ove Røsstad Holding AS | Financial services | 2005 |
| Overblikk AS | Agriculture & fishing | 2009 |
| Oxford Research AS | Professional & scientific | 2004 |
| Oxidane Markets AS | Information & communication | 2020 |
| Oxidane Technologies AS | Information & communication | 2021 |
| Oxidane Venture AS | Information & communication | 2020 |
| OY Checkmark Ltd Nuf | Wholesale & retail | 2020 |
| Ozeta AS | Manufacturing | 2020 |
| Olavsbyggene AS | Households | 1951 |
| P&S-Itech AS | | 2017 |
| P-S Invest AS | Real estate | 2005 |
| P.Langfeldt Invest AS | Professional & scientific | 2025 |
| P4B Licenses AS | Professional & scientific | 2013 |
| Pa Bjørnstad Holding AS | | 2020 |
| Pa Mur AS | Construction | 2011 |
| Paala Invest AS | | 2021 |
| Paaloma AS | Professional & scientific | 2022 |
| Paasche AS | Health & social care | 2023 |
| Pactor AS | Financial services | 2005 |
| Padel Sør AS | Education | 2019 |
| Padilla Newco AS | Real estate | 2025 |
| Paga AS | Professional & scientific | 2009 |
| Pagels AS | Information & communication | 2017 |
| Paint on Pots Kristiansand AS | Wholesale & retail | 2026 |
| Pak Invest AS | Real estate | 2005 |
| Pakkenellik AS | Information & communication | 2024 |
| Pakon AS | Professional & scientific | 2020 |
| Palatino AS | Real estate | 2004 |
| Palestinabutikken Jafra AS | Wholesale & retail | 2025 |
| Palett Invest AS | Construction | 2005 |
| Palle Rosenkrantz Gate 15 AS | Real estate | 2011 |
| Palma Musikkbar Ans | Hospitality | 1997 |
| Palmcoast Shipping & Invest AS | Professional & scientific | 2026 |
| Palmesus AS | Arts & recreation | 2016 |
| Palmesus Holding AS | | 2025 |
| Palmyra AS | Construction | 2021 |
| Paloma AS | Real estate | 2004 |
| Pan M Records Ans | Arts & recreation | 2000 |
| Pant AS | | 2020 |
| Panteon AS | Information & communication | 2014 |
| Paper Stack International AS | Wholesale & retail | 2019 |
| Papirkort AS | Wholesale & retail | 2017 |
| Para AS | Professional & scientific | 2013 |
| Paradox Invest AS | Arts & recreation | 2004 |
| Parajam Records Da | Information & communication | 2017 |
| Paral Dynamic AS | Information & communication | 2023 |
| Paranova AS | Wholesale & retail | 1994 |
| Pareto Shipbrokers AS | Transport & logistics | 1990 |
| Parken Antirust AS | Other services | 2019 |
| Parken Bilutleie AS | Administrative & support | 2002 |
| Parken Karosseri AS | Other services | 2019 |
| Parko Grillen AS | Hospitality | 2023 |
| Part Holding AS | Financial services | 2005 |
| Partner Bio AS | Energy | 2021 |
| Partner Energy AS | Construction | 2019 |
| Partner Sør Eiendomsutvikling AS | Real estate | 2016 |
| Partner-Eiendom M56 AS | Real estate | 2017 |
| Partum Nubes AS | Information & communication | 2022 |
| Party Grill AS | Hospitality | 2023 |
| Parvus Retail Consult AS | Professional & scientific | 2015 |
| Pascal Eiendom AS | Real estate | 2006 |
| Pasimima Holding AS | | 2022 |
| Passiv Energi AS | Construction | 2012 |
| Path AS | Real estate | 2020 |
| Pathummas Massasje AS | Other services | 2020 |
| Pattra Thaimat AS | Hospitality | 2022 |
| Paula AS | Wholesale & retail | 2019 |
| Paulen AS | Real estate | 2013 |
| Paulen Invest AS | Administrative & support | 2006 |
| Pauschert & Co AS | Administrative & support | 2026 |