| Oliven Invest AS | | 2026 |
| Olivis AS | Wholesale & retail | 2023 |
| Oljestein AS | Construction | 2026 |
| Ollmann Eiendom AS | Real estate | 2025 |
| Olsbø & Paulsen AS | Construction | 1985 |
| Olsen Batterier AS | Wholesale & retail | 1987 |
| Olsen Innstallasjon AS | Construction | 2013 |
| Olsvika Eiendom AS | Real estate | 2000 |
| Olsvikskaret Eiendom AS | Real estate | 2008 |
| Omegasenteret AS | Real estate | 1995 |
| Omfram AS | | 2020 |
| Omkl Holding AS | Construction | 2018 |
| Omn Bygg AS | Construction | 2025 |
| On Import AS | Wholesale & retail | 2020 |
| On the Road Again AS | Wholesale & retail | 2023 |
| Onli Svømmehallen Fysioterapi Da | Health & social care | 1997 |
| Ono Invest AS | Professional & scientific | 2020 |
| Onym AS | Information & communication | 2013 |
| Onyx NO1 AS | Professional & scientific | 2019 |
| Openbridge Components AS | Information & communication | 2024 |
| Oppigaard AS | Real estate | 2022 |
| Opsahl Og Larsen & Co Da | Manufacturing | 1990 |
| Optiker Nelvik Moa AS | Wholesale & retail | 1998 |
| Optiker Nelvik Ålesund AS | Wholesale & retail | 1999 |
| Optimum Kiropraktikk AS | Health & social care | 2014 |
| Orange Aerial AS | Information & communication | 2009 |
| Orient Agentur Ans | Wholesale & retail | 1995 |
| Orion Eiendom AS | Real estate | 1998 |
| Orion Seafood AS | Wholesale & retail | 2012 |
| Orkide Andersen Frisør AS | Other services | 2014 |
| Ors Holding AS | Real estate | 2021 |
| ORS1 AS | Real estate | 2022 |
| ORS2 AS | Real estate | 2022 |
| Os Kapital AS | | 2026 |
| Osa Invest AS | Professional & scientific | 2005 |
| Osc AS | Information & communication | 2004 |
| Oscar Larsen AS | Real estate | 2005 |
| Oscar Larsen Eiendom AS | Real estate | 1918 |
| Oscar Rørhuus AS | Real estate | 1925 |
| Oscorp AS | Professional & scientific | 2012 |
| Oseberg Finans AS | Administrative & support | 2004 |
| Oslof AS | Real estate | 1990 |
| Osov Holding AS | Information & communication | 2024 |
| Otalmo Holding AS | | 2019 |
| Otlav Holding AS | Administrative & support | 2011 |
| Otlo Holding AS | | 2015 |
| Otlo Invest AS | Professional & scientific | 2005 |
| Ottar Flydal AS | Real estate | 1990 |
| Ottar Myklebust Anlegg AS | Construction | 2025 |
| Otterlei Io AS | Information & communication | 2023 |
| OWI-SUB1 AS | Transport & logistics | 2025 |
| Oyvo Invest AS | Real estate | 2018 |
| P & O Offshore Services Pte Ltd | Transport & logistics | 1997 |
| P D Stafseth AS | Wholesale & retail | 1992 |
| P Juls Sandvig AS | Manufacturing | 2018 |
| P Juls Sandvig Eiendom AS | Manufacturing | 1987 |
| P&O Maritime Services (UK) Ltd | Transport & logistics | 2002 |
| P. Iversen Invest AS | Financial services | 2017 |
| P.P.U.H Stabi-L Boguslaw Hendel | Construction | 2011 |
| P.R Invest AS | | 2026 |
| Pab Consulting AS | Professional & scientific | 1993 |
| Pagro AS | Wholesale & retail | 2021 |
| Palander AS | Professional & scientific | 1999 |
| Palander Holding AS | Professional & scientific | 1993 |
| Palmtree Productions AS | Information & communication | 2019 |
| Pama Helse AS | Health & social care | 2024 |
| Panoramica AS | Professional & scientific | 2017 |
| Parcel AS | | 2020 |
| Parkettsystem AS | Construction | 2016 |
| Parkgata 14 AS | Real estate | 1995 |
| Parkgata 3 Ålesund AS | Real estate | 2001 |
| Parkgaten 4 AS | Real estate | 2020 |
| Parkly AS | Information & communication | 2019 |
| Party Vest AS | Wholesale & retail | 2022 |
| Pas Invest AS | Manufacturing | 2005 |
| Paso AS | Professional & scientific | 2005 |
| Pataxos AS | Real estate | 2000 |
| Patogen AS | Professional & scientific | 2003 |
| Paul's Flisleggerfirma AS | Construction | 2024 |
| Paulsen Eiendomsinvest AS | Real estate | 2020 |
| Paulsen-Eiendom AS | Real estate | 1997 |
| Pecunius AS | | 2025 |
| Peder Naalsund AS Transportforretning | Transport & logistics | 1980 |
| Peder Øie AS | Wholesale & retail | 1999 |
| Peding Holding AS | Financial services | 2013 |
| Peer Gynt Galleriet AS | Wholesale & retail | 2004 |
| Peggeo AS | Hospitality | 2024 |
| Peil AS | Professional & scientific | 2000 |
| Pelfisk AS | Agriculture & fishing | 1996 |
| Pemana AS | | 2020 |
| Pengebalanse AS | Professional & scientific | 2023 |
| People Mode AS | Professional & scientific | 2023 |
| Per Græsdal AS | Real estate | 2012 |
| Perane AS | Professional & scientific | 1998 |
| Perspektiv Samtaleterapi & Veiledning AS | Health & social care | 2020 |
| Pesquera Lota Protein Ltda | Manufacturing | 2003 |
| Peter Skarbøvig AS | Agriculture & fishing | 2017 |
| Petriop AS | | 2024 |
| Petro Well Services AS | Mining & quarrying | 2016 |
| Pettersen & Nystøyl Holding AS | Real estate | 2011 |