| Stall Hansen AS | Arts & recreation | 2013 |
| Stamsaas Company AS | Real estate | 2009 |
| Stang & Stang Ans | Agriculture & fishing | 2003 |
| Stang Og Skjelle Da | Agriculture & fishing | 1994 |
| Stansefabrikken Home AS | Wholesale & retail | 2019 |
| Stansefabrikken Solutions AS | Manufacturing | 1979 |
| Star Investering AS | Real estate | 2002 |
| Stasjonsdrift Pedersen AS | Wholesale & retail | 2023 |
| Statsminister Kolstadsvei 1-3 AS | Real estate | 1991 |
| Stiga Eiendom AS | Real estate | 2012 |
| Stiga Entreprenør AS | Construction | 2020 |
| Stiga Invest AS | Professional & scientific | 2017 |
| Stiga Konsult AS | Professional & scientific | 2002 |
| Stiga Prosjekt AS | Real estate | 2015 |
| Strai Kjøkken Sarpsborg AS | Wholesale & retail | 2003 |
| Strands Utleie AS | Administrative & support | 2022 |
| Strigoo AS | Information & communication | 2019 |
| Studio X AS | Information & communication | 2018 |
| Støttespilleren AS | Administrative & support | 2015 |
| Svartbekk Eiendom AS | Real estate | 1927 |
| Svartedal AS | Professional & scientific | 2020 |
| SVP Consulting AS | Professional & scientific | 2025 |
| SYSTEM1 AS | Construction | 2005 |
| Sæthrum AS | | 2020 |
| TAKSTKONSULENT1 AS | Real estate | 2019 |
| Tangen Gruppen AS | Real estate | 2023 |
| Tangen-Eiendom AS | Real estate | 2023 |
| Tannlege Ådalen AS | Health & social care | 2024 |
| Tannlegene Arne Morvik & Christin Borgmo Ans | Health & social care | 2005 |
| TCB Horses AS | Agriculture & fishing | 2026 |
| Team Trade AS | Professional & scientific | 1998 |
| Techsphere Solutions AS | Information & communication | 2023 |
| Techwave Solutions AS | Information & communication | 2014 |
| Tek-Eiendom AS | Real estate | 2007 |
| Tek-Eiendom II AS | Real estate | 2007 |
| Tek-Eiendom IV AS | Real estate | 2025 |
| Telink AS | Information & communication | 2026 |
| Thomas Mareno Holding AS | | 2024 |
| Tindlund Eiendom AS | Real estate | 2014 |
| Tju Consulting AS | Financial services | 2012 |
| Tobben's Varmepumpeservice AS | Construction | 2014 |
| Toha Invest AS | Financial services | 2017 |
| Tole Holding AS | | 2020 |
| Toll Holding AS | Construction | 2005 |
| Tombre Holding AS | | 2023 |
| Tordenskiolds Kvartalet AS | Real estate | 2016 |
| Torp Næring AS | Real estate | 2006 |
| Tr/T Holding AS | Construction | 2023 |
| Triton Norway Holding | | 2019 |
| Trylle Eiendom AS | Real estate | 2006 |
| Tubus Holding AS | Professional & scientific | 2005 |
| Tune Eiendom AS | Real estate | 1987 |
| Tune Eiendomsselskap AS | Real estate | 1987 |
| Tune Fysioterapi Da | Health & social care | 2011 |
| Tune Legesenter AS | Health & social care | 2013 |
| Tune Mat AS | Hospitality | 2012 |
| Tune Senter AS | Real estate | 1992 |
| Tveter VVS AS | Construction | 2026 |
| Unopax AS | Professional & scientific | 2015 |
| Vaia AS | Manufacturing | 2005 |
| Vaia Eiendom AS | Real estate | 2013 |
| Vaia Miljø AS | Professional & scientific | 2020 |
| Versatile Solutions AS | Information & communication | 2023 |
| Vestlia Bolig AS | Real estate | 2007 |
| Viavi Solutions Norway Nuf | Wholesale & retail | 1995 |
| Viddex AS | | 2020 |
| Viken Audio AS | Administrative & support | 2014 |
| Viken Bygg Og Maskin AS | Professional & scientific | 2020 |
| Villaveien 9 AS | Real estate | 2026 |
| Viridis AS | Construction | 2020 |
| Viridis Eiendom AS | | 2024 |
| VR Eiendom AS | Real estate | 2025 |
| Vysion AS | Professional & scientific | 2026 |
| Waldemar Podwojski Firma Wadex | Construction | 2006 |
| Westlind Invest AS | | 2023 |
| White Label AS | Professional & scientific | 2017 |
| Wilskog Holding AS | Wholesale & retail | 2005 |
| Winther Holding AS | Financial services | 2005 |
| WL Holding AS | Real estate | 2005 |
| Yoho Holding AS | | 2025 |
| Zephyr AS | Energy | 2006 |
| Zephyr Prosjekt AS | Energy | 2024 |
| Ådalen Bygg Og Eiendom AS | Construction | 2017 |
| Ådalen Rental AS | Administrative & support | 2023 |
| Ådalen Tombre Holding AS | Professional & scientific | 2018 |
| Ådalen Truck AS | Wholesale & retail | 2005 |
| Ådalen Utleie AS | Administrative & support | 2022 |
| Åkebergmosen Eiendom AS | Real estate | 2016 |
| Øistein AS | Information & communication | 2008 |
| Økonomi-Deler AS | Wholesale & retail | 1973 |
| Ørst Invest AS | Financial services | 2010 |
| Øst Eiendomsutvikling AS | Real estate | 2005 |
| Østermark Holding AS | Financial services | 2015 |
| Østfold Bildemontering AS | Wholesale & retail | 2001 |
| Østfold Eiendomsutleie AS | Real estate | 1998 |
| Østfold Energi AS | Energy | 1998 |
| Østfold Energi Solkraft AS | | 2024 |
| Østfold Energi Vekst AS | | 2024 |
| Østfold Energi Vindkraft AS | Energy | 2003 |
| Østfold Fjellsprenging AS | Construction | 2024 |