| Å Energi Fornybar Forvaltning AS | Energy | 2012 |
| Å Energi Havvind AS | Energy | 2023 |
| Å Energi Invest AS | Information & communication | 2005 |
| Å Energi SN2 Holdco AS | Energy | 2023 |
| Å Energi Un Holdco AS | Energy | 2023 |
| Å Energi Utvikling AS | Energy | 2001 |
| Å Energi Vannkraft AS | Energy | 2001 |
| Å Energi Varme AS | Energy | 1999 |
| Ågrè Holding AS | Wholesale & retail | 2015 |
| Ånund Lunde AS | Real estate | 2003 |
| Ånund Lunde Eiendom AS | Real estate | 2020 |
| Åpne & Lukke AS | Wholesale & retail | 2014 |
| Åpne Barnehager AS | Education | 2005 |
| Åra Vann Og Kloakk SA | Water & waste | 2015 |
| Ås Invest AS | | 2020 |
| Åsane Mat AS | Wholesale & retail | 2001 |
| Åsen Øvrebø Eiendom AS | Real estate | 2005 |
| Åsli Invest AS | Real estate | 2017 |
| Åttifire AS | Health & social care | 2024 |
| Åttito AS | | 2025 |
| Åvik Brygge AS | Real estate | 2007 |
| Ægirs Vei 1 AS | Real estate | 2024 |
| Ægirsvei 10B AS | Real estate | 2021 |
| Ægirsvei 2-6 AS | Real estate | 2003 |
| Ægirsvei Eiendom AS | Real estate | 2011 |
| Ø S 46 Invest AS | Real estate | 2014 |
| Ø-Hus AS | Professional & scientific | 2019 |
| Øab Holding AS | Financial services | 2005 |
| Øch Invest AS | Mining & quarrying | 1998 |
| Øde Øya X AS | Administrative & support | 2024 |
| Øde Øya XXX AS | Information & communication | 2024 |
| Ødegård Utvikling AS | Real estate | 2015 |
| Øgrey Landmark Holding AS | Real estate | 2019 |
| Øh Kapital AS | Real estate | 2019 |
| Øidna Bygg AS | Construction | 2015 |
| Øien & Bjorvatn Filmproduksjon AS | Information & communication | 1997 |
| Øko AS | Construction | 2020 |
| Økoconsult AS | Professional & scientific | 1998 |
| Øksendal Management AS | Professional & scientific | 2012 |
| Ølboden AS | Wholesale & retail | 2026 |
| Ølkongen På Sørlandet AS | Wholesale & retail | 2020 |
| Øma AS | Real estate | 2022 |
| Ørjan Holding AS | | 2015 |
| Ørt Invest AS | | 2021 |
| Øs 12 Invest AS | Real estate | 2013 |
| Østanne AS | Real estate | 2018 |
| Østensvik Holding AS | | 2021 |
| Østerveien 10 Eiendom AS | Real estate | 2025 |
| Østerveien 21 AS | Real estate | 2014 |
| Østerveien 23 AS | Real estate | 2019 |
| Østfold Tak Og Fasadevask AS | Administrative & support | 2025 |
| Østre No 5 AS | Real estate | 2020 |
| Østre Strandgate 11 AS | Real estate | 2019 |
| Østre Strandgate 13-15 AS | Real estate | 2023 |
| Østre Strandgate 31 AS | Real estate | 2006 |
| Østre Strandgate 38-40 Invest AS | Real estate | 2021 |
| Østre Strandgate 41A AS | Real estate | 2020 |
| Østre Strandgate 5 AS | Real estate | 2015 |
| Østre Strandgate 80 AS | Real estate | 2009 |
| Østre Strandgate Eiendom AS | Real estate | 2014 |
| Østsia AS | Construction | 2019 |
| Østsia Trafikkskole AS | Education | 2023 |
| Østsiden Glasservice AS | Construction | 2012 |
| Østsiden Holding AS | Wholesale & retail | 2005 |
| Øts AS | Financial services | 2005 |
| Øven Holding AS | Financial services | 2005 |
| Øvensen Flis AS | Construction | 2013 |
| Øveråsen Transport AS | Transport & logistics | 2021 |
| Øvland Designstudio AS | Professional & scientific | 2026 |
| Øvre Eikervei 122 AS | Real estate | 2011 |
| Øvre Eikervei 126 AS | Real estate | 2006 |
| Øvre Timenes AS | Agriculture & fishing | 2021 |
| Øya Film AS | Information & communication | 2015 |
| Øya Interaktiv AS | Information & communication | 2015 |
| Øyelege Eckhoff AS | Health & social care | 2019 |
| Øyelege Fischer AS | Health & social care | 2008 |
| Øystein Torsås AS | Information & communication | 2021 |
| Øyvind Arnesen AS | Professional & scientific | 1994 |
| Øyvind Frøyland Holding AS | Education | 2014 |
| Øyvind Selbek Holding AS | | 2025 |
| Øyvor AS | Professional & scientific | 2022 |