| TDP Invest AS | | 2025 |
| Tecnovap AS | Professional & scientific | 2011 |
| Tekkam AS | Financial services | 2005 |
| Tellus Østfold AS | Wholesale & retail | 1998 |
| Temco AS | Professional & scientific | 2012 |
| Terrawatt AS | Professional & scientific | 2019 |
| Thomas Myhra Graving Og Transport AS | Construction | 2020 |
| Thoresens Brille Og Kontaktlinsesenter AS | Wholesale & retail | 1980 |
| Thorvaldsen Holding AS | Arts & recreation | 2011 |
| Tibi Eiendom AS | Real estate | 2022 |
| Tma Bygg AS | Construction | 2021 |
| Tofteberg AS | Manufacturing | 2021 |
| Tom Sørum Transport AS | Transport & logistics | 2022 |
| Torkildstad Vei-, Vann- Og Avløpslag SA | Water & waste | 2014 |
| Torvbanen 10 AS | Real estate | 2021 |
| Torvbanen 12 AS | Real estate | 2025 |
| Torvbanen 8 AS | Real estate | 2021 |
| Torvstikkeren 6 AS | Real estate | 2019 |
| Totembygg AS | Construction | 2025 |
| Tredim AS | Information & communication | 2006 |
| Trend Shop AS | Wholesale & retail | 2003 |
| Trikks AS | Information & communication | 2011 |
| Tronds Bygg AS | Construction | 2016 |
| Truckfix AS | Manufacturing | 2026 |
| Trykkern AS | Manufacturing | 2016 |
| Tvetes Tavernette AS | Hospitality | 2021 |
| Ultra Facility AS | Construction | 2019 |
| Unel Eiendom AS | | 1993 |
| Unimark Tutaj AS | Construction | 2019 |
| Vardestubben AS | Construction | 2018 |
| Veggli Fjellgrend AS | Real estate | 2024 |
| Veidec Norge AS | Wholesale & retail | 2010 |
| Vendingrobotics AS | Wholesale & retail | 2019 |
| Veos AS | Transport & logistics | 2026 |
| Veridion Dynamics AS | Information & communication | 2024 |
| Vestby Holding AS | | 2023 |
| Vestbygda Va Drift SA | Water & waste | 2021 |
| Vestbygda Va Utbygging SA | Water & waste | 2021 |
| Viasano AS | Information & communication | 2023 |
| Vifitrans AS | Transport & logistics | 2018 |
| Vigli AS | Real estate | 2017 |
| Vinporten AS | Wholesale & retail | 2025 |
| Vinus Kebab AS | Hospitality | 2013 |
| Vinus Kebab Råde Da | Hospitality | 2023 |
| Vital Bygg AS | Construction | 2011 |
| Vital Eiendomsutvikling AS | Construction | 2011 |
| Vital Prosjekt AS | Real estate | 2016 |
| Weels Betong & Plast AS | Wholesale & retail | 1997 |
| Weels Eiendom AS | Real estate | 2005 |
| Williams Caravan AS | Wholesale & retail | 2016 |
| Williams Holding AS | Real estate | 1998 |
| Wold Autoservice Ans | Wholesale & retail | 2003 |
| Wæraas Invest AS | Real estate | 1997 |
| Ya Service AS | Transport & logistics | 2020 |
| Zero Gravity AS | Professional & scientific | 2023 |
| Åkebergmosen 12 AS | Real estate | 2013 |
| Åkebergmosen 82-64 AS | Real estate | 2008 |
| Øb Landmåling Og Byggkontroll AS | Professional & scientific | 2025 |
| Økonomitjenester Tangen AS | Professional & scientific | 2019 |
| Ørmen Dekkbark AS | Wholesale & retail | 2001 |
| Øst Maskindrift AS | Construction | 2026 |
| Øst-Revisjon BFT AS | Professional & scientific | 2017 |
| Østbygda Vanningslag SA | Agriculture & fishing | 1995 |
| Østfold Mur Og Flis AS | Construction | 2016 |
| Østfold Overflateteknikk AS | Construction | 2013 |
| Østfold Sten AS | Construction | 2021 |
| Østlandske Bilauksjon AS | Real estate | 1984 |