| Alven Books AS | Information & communication | 2018 |
| Am Betongsaging AS | Construction | 2021 |
| Am Eiendom Invest AS | Real estate | 2008 |
| Amahan AS | | 2025 |
| Amal Holding AS | Transport & logistics | 2021 |
| Amfi Medisinske Senter AS | Health & social care | 2025 |
| Amicivitae AS | Administrative & support | 2012 |
| Amlo/Nilsen AS | Real estate | 2015 |
| Anator AS | Information & communication | 2017 |
| Ancamar AS | Professional & scientific | 2024 |
| Andelshagebruket Røed På Jeløy SA | Wholesale & retail | 2016 |
| Anders Tonholt AS | Real estate | 2005 |
| Andorsen AS | Information & communication | 1966 |
| Andreassen Invest AS | | 2019 |
| Anfa Eiendom AS | Real estate | 2022 |
| Angell Realestate AS | Real estate | 2020 |
| Anglo Supply AS | Wholesale & retail | 1989 |
| Anleggsutstyr Øst Ans | Wholesale & retail | 2015 |
| Anleggsutstyr Øst AS | Real estate | 2017 |
| Anm Holding AS | | 2026 |
| Ann Kristin Børresen AS | Wholesale & retail | 2010 |
| Anna Beauty Studio AS | Other services | 2024 |
| Anna Cava Holding AS | Professional & scientific | 2021 |
| Anniken Holding AS | Real estate | 2016 |
| Anomaly Holding AS | | 2022 |
| Anova Boliger AS | Construction | 2009 |
| Anova Boliger Eiendom AS | Real estate | 2012 |
| Ans Strikkemor Ellen Olavesen & Co | Wholesale & retail | 1987 |
| Antho AS | Construction | 2022 |
| Anto Invest AS | | 2016 |
| Antonsen Bil AS | Wholesale & retail | 2026 |
| Anvendia AS | Information & communication | 2007 |
| Aoe Eiendom AS | Wholesale & retail | 2017 |
| Aoe Holding AS | Other services | 2017 |
| Apax Holding AS | Real estate | 2007 |
| April Invest AS | | 2024 |
| Apropo AS | Hospitality | 2019 |
| Apteka AS | Wholesale & retail | 2024 |
| Aquarius Dykkerskole Da | Wholesale & retail | 1988 |
| Arbeiderboligene Ans | Real estate | 1990 |
| Architect AS | Professional & scientific | 2026 |
| Arctic Protein AS | Wholesale & retail | 2011 |
| Arctic Rainforest Ans | Wholesale & retail | 2000 |
| Arctic Software AS | Information & communication | 2021 |
| Are Karlsen AS | Wholesale & retail | 2004 |
| Areal Asfalt AS | Construction | 2026 |
| Areal Asfalt Holding AS | Real estate | 2021 |
| Areal Maskin AS | Construction | 2021 |
| AREAL101 AS | Real estate | 2018 |
| Arild Golf Academy AS | Education | 2023 |
| Arkadia Ans | Administrative & support | 2002 |
| Arkitekt AS | Professional & scientific | 2017 |
| Arkitekt Atle Leira AS | Professional & scientific | 2015 |
| Arkitekturverket AS | Professional & scientific | 2012 |
| Arkverk AS | Professional & scientific | 2026 |
| Armana Holding AS | Professional & scientific | 2014 |
| Arx Digitalis AS | Information & communication | 2026 |
| AS Betongpumping | Construction | 2018 |
| AS Dronningensgate 27 | Real estate | 1959 |
| AS Hans Børstadsvei 10-12 | Real estate | 1976 |
| AS Husselskapet | Real estate | 1953 |
| AS Mjelde | Real estate | 1964 |
| AS Montebello Group | Professional & scientific | 2017 |
| AS Moss Transportforum | Transport & logistics | 1986 |
| AS Refsnes Eiendomsselskap | Real estate | 1977 |
| AS Rygge Tomteselskap | Real estate | 1966 |
| AS Silva | Agriculture & fishing | 1910 |
| AS Varnaveien 7 | Real estate | 1984 |
| Aselo Holding AS | | 2021 |
| Asian Finds AS | Hospitality | 2025 |
| Askar Invest AS | Real estate | 2019 |
| Askautrud Holding AS | | 2019 |
| Askim Torg AS | Real estate | 2020 |
| Askonor AS | Real estate | 1998 |
| Asp Holding AS | Information & communication | 1999 |
| Asteri AS | | 2024 |
| Astranova Holding AS | | 2024 |
| Astrid Solberg Holding AS | | 2024 |
| At Eiendom Moss AS | Real estate | 2017 |
| At Sandnes Holding AS | | 2023 |
| Atelièr Agapi AS | Wholesale & retail | 2021 |
| Atem AS | Real estate | 2019 |
| Atlet AS | Professional & scientific | 2025 |
| Aton Solenergi AS | Construction | 2023 |
| Atracco AS | Wholesale & retail | 2002 |
| Audiatur Bokhandel AS | Wholesale & retail | 2015 |
| Audioco AS | Wholesale & retail | 2018 |
| Augerød Butikk Eiendom AS | Real estate | 2017 |
| Augerød Utvikling AS | Real estate | 2011 |
| Auntie Norge AS | Health & social care | 2022 |
| Aurelian Art. 001 AS | Manufacturing | 2026 |
| Aurelian Manufacturing AS | Professional & scientific | 2025 |
| Auremira Holding AS | | 2025 |
| Aurora Capital Group AS | Transport & logistics | 2021 |
| Aurora Omsorg AS | Health & social care | 2019 |
| Auto Vault AS | Wholesale & retail | 2016 |
| Autofix Bilsalg AS | Wholesale & retail | 2025 |
| Autofix Moss AS | Other services | 2013 |
| Autofix Verksted AS | Other services | 2025 |
| Autokompaniet AS | Wholesale & retail | 2012 |