| 33 Street Food Fredrikstad AS | Hospitality | 2025 |
| A/S Mascot Holding | Wholesale & retail | 1988 |
| Aaj Invest AS | | 2019 |
| Acutus AS | Construction | 2020 |
| Af Consult Management AS | Real estate | 1976 |
| Afh Consult AS | Health & social care | 2021 |
| Agro & Miljø AS | Construction | 2006 |
| Ainima Holding AS | | 2022 |
| Aiuto Tech AS | Information & communication | 2026 |
| Aktium Albert Moeskaus Vei 37 AS | Real estate | 2026 |
| Aktium Boligutvikling AS | Real estate | 2021 |
| Aktium Eiendom AS | Professional & scientific | 2018 |
| Aktium Entreprenør AS | Real estate | 2016 |
| Aktium Forvaltning AS | Real estate | 2014 |
| Aktium Gamle Ålevei 115 AS | Real estate | 2024 |
| Aktium Geithus AS | Real estate | 2025 |
| Aktium Holding AS | Real estate | 2010 |
| Aktium Invest AS | Real estate | 2022 |
| Al Elektriske AS | Construction | 1993 |
| Al-Product Brødr Larsen Ans | Manufacturing | 1985 |
| Alhambra 8 AS | Real estate | 2025 |
| Alma Klær AS | Wholesale & retail | 2018 |
| Alneshms AS | Health & social care | 2026 |
| Alpha-Derma Norge AS | Wholesale & retail | 2003 |
| Altocumulus Holding AS | | 2021 |
| Am Mur Og Betong AS | Construction | 2022 |
| Am Peis & Pipe AS | Construction | 2024 |
| Amka Flex AS | Administrative & support | 2019 |
| Andersen Og Fjelle Da | Agriculture & fishing | 2006 |
| Andersen Og Heie Eiendom AS | | 2001 |
| Andersen Transport Ans | Transport & logistics | 1988 |
| Andreassen Og Larsen Elektriske Ans | | 1990 |
| Anker-Holding AS | | 2023 |
| Ans Onsøy Solsenter | | 1986 |
| Antik Og Brukt Centralen AS | Wholesale & retail | 2018 |
| Antonsen Entreprenør AS | Construction | 2004 |
| Ao Eiendomsselskap AS | Real estate | 2016 |
| Arild Sten Larsen AS | Real estate | 2019 |
| Arne Nilsen Holding AS | | 2022 |
| Aronsen Booking & Management AS | Professional & scientific | 2026 |
| Artéfa AS | Wholesale & retail | 2025 |
| AS Båtbua | Wholesale & retail | 1987 |
| AS Decim | Real estate | 1987 |
| AS Diamantboring | Construction | 1975 |
| AS Diamantboring Unicon | Wholesale & retail | 1989 |
| AS Oljelagring | Transport & logistics | 1943 |
| Ashton Burke Services Nuf | Administrative & support | 2014 |
| ASKVOLL HANDEL ANS Bjørn og Torill Andreassen | Wholesale & retail | 1989 |
| Aspelundveien 2 AS | Real estate | 2025 |
| Aspelundveien 4 AS | Real estate | 2017 |
| Assuransetakst AS | Real estate | 2020 |
| Atg Services AS | Agriculture & fishing | 2015 |
| Atm Konsult AS | | 2023 |
| Autopartner Fredrikstad AS | Wholesale & retail | 1998 |
| Autopartner Fredrikstad Eiendom AS | Real estate | 2010 |
| Autoservice Fredrikstad AS | Other services | 1998 |
| Avfallsrett AS | Professional & scientific | 2020 |
| Avretting AS | Construction | 2019 |
| Azh Holding AS | | 2019 |
| B&O Utvikling AS | Real estate | 2023 |
| Baba Eiendom AS | Real estate | 2025 |
| Backyard Engineering AS | Wholesale & retail | 2019 |
| Bak Fasaden Samtaleklinikk AS | Education | 2026 |
| Bare Assets AS | Real estate | 2018 |
| Barnelivet Da | Wholesale & retail | 2024 |
| Bavida AS | Wholesale & retail | 2016 |
| Bekkevold Murerservice AS | Construction | 2024 |
| Bekkhus Consulting AS | Professional & scientific | 2020 |
| Bemik Consult AS | Professional & scientific | 2014 |
| Benedicte Gundersen AS | Education | 2004 |
| Bercato Produkter AS | Wholesale & retail | 2005 |
| Bergdal AS | Real estate | 1990 |
| Bergum & Steen Eiendom AS | Real estate | 2015 |
| Bergum Bygg AS | Construction | 2014 |
| Best Byggtjenester AS | Construction | 2025 |
| Bevares AS | Real estate | 2005 |
| Bewi Insulation Norge AS | Manufacturing | 1956 |
| Bjerke AS | Real estate | 2002 |
| Bjerkedal Skog Da | Agriculture & fishing | 2011 |
| Bjørkelo AS | | 2020 |
| Bjørklund Bygg & Eiendom AS | Real estate | 1989 |
| Blaasopp AS | Information & communication | 2014 |
| Blinken AS | Wholesale & retail | 1981 |
| Blue Ocean Media AS | Information & communication | 2020 |
| Bluerise Group AS | Wholesale & retail | 2025 |
| Bmedia AS | Professional & scientific | 2026 |
| Bms-Invest AS | Construction | 1991 |
| BMT Holding AS | | 2019 |
| Bo Holding AS | Real estate | 2015 |
| Boks 84 AS | Real estate | 1984 |
| Booster AS | Manufacturing | 2021 |
| Borg Eiendom Og Holding AS | Real estate | 2013 |
| Borge Miljøservice AS | Construction | 2020 |
| Boutique Maman AS | Wholesale & retail | 2003 |
| BOX1 AS | Arts & recreation | 2008 |
| Bratt Jensen Eiendom AS | Real estate | 2025 |
| Bratt Jensen Holding AS | | 2024 |
| Brudevold Og Huth AS | Construction | 2025 |
| Bruket 35 AS | Arts & recreation | 2010 |
| Bruket 39 AS | Administrative & support | 2025 |