| Steverton AS | Real estate | 2013 |
| Stian & Meller Holding AS | Arts & recreation | 2019 |
| Stian & Meller Studio AS | Arts & recreation | 2019 |
| Stilla AS | | 2025 |
| Stillits AS | Professional & scientific | 2025 |
| Stoker Invest AS | Real estate | 2006 |
| Stokker Bygg AS | Professional & scientific | 2008 |
| Storgaten 18 Drøbak AS | Real estate | 2015 |
| Storgaten AS | Real estate | 2015 |
| Stormåsan AS | Real estate | 2022 |
| Strategi Pilot AS | Professional & scientific | 2024 |
| Strålsundtangen Vann- Og Avløpslag SA | Water & waste | 2021 |
| Studio Haver AS | Professional & scientific | 2012 |
| Studiobo Eiendom AS | Real estate | 2009 |
| Studiotjueèn AS | Other services | 2025 |
| Styrehjelp AS | Professional & scientific | 2019 |
| Støre Ventures AS | Professional & scientific | 2022 |
| Su Casa Café AS | Hospitality | 2023 |
| Subtrackr AS | Information & communication | 2019 |
| Sufus Holding AS | | 2022 |
| Sun Side Invest & Consult AS | Real estate | 1988 |
| Sunn Finans AS | Professional & scientific | 2024 |
| Sustainability Engineering Centre AS | Professional & scientific | 2022 |
| Svalestien AS | Arts & recreation | 2023 |
| Svensk Trefiber AS | Construction | 2018 |
| Sverdvik & Co AS | | 2024 |
| Sverre Aam Holding AS | | 2025 |
| Svevik AS | Real estate | 2019 |
| Svingen AS | Households | 1979 |
| Swan Noir Invest AS | | 2009 |
| Synapsis AS | | 2025 |
| Sølvberg Tekstil AS | Wholesale & retail | 1956 |
| Sølvskje Holding AS | Real estate | 2020 |
| Søndre Ekeberg Vann Og Avløp SA | Water & waste | 2019 |
| Sørbråtenveien Avløpslag SA | Water & waste | 2014 |
| Sørbye Invest AS | | 2020 |
| Sørconsult AS | Professional & scientific | 2017 |
| Sørlund AS | Health & social care | 2012 |
| Tae Invest AS | Hospitality | 2007 |
| Tag AS | Hospitality | 1988 |
| Takhar Investment AS | Real estate | 2017 |
| Takstmann Roy Bekkesletten AS | Professional & scientific | 2014 |
| Takstmannen AS | Professional & scientific | 2013 |
| Tangentoppen AS | Real estate | 2017 |
| Tanib Holding AS | | 2022 |
| Tannlege Bjørn Einar Dahl AS | Health & social care | 2006 |
| Tannlegene Qvale AS | Health & social care | 2022 |
| TBH AS | Professional & scientific | 2015 |
| TBH Eiendom AS | Real estate | 2019 |
| TBH Eiendom Østfold AS | Real estate | 2020 |
| Teda AS | Real estate | 2013 |
| Tehuset.No Ans | Wholesale & retail | 2012 |
| Telcall AS | Wholesale & retail | 2002 |
| Telcofy AS | Information & communication | 2025 |
| Telekiosken Drøbak AS | Wholesale & retail | 1997 |
| Temof AS | Other services | 2019 |
| Tempodia AS | Financial services | 1958 |
| Tenbagger AS | Information & communication | 2022 |
| Tenera Invest AS | Financial services | 2021 |
| Tengo Invest AS | Financial services | 2014 |
| Teper AS | Real estate | 1991 |
| Tepto Import AS | | 1994 |
| Tera Montaze Sro | Administrative & support | 2011 |
| Tertitten Barnehage Ans | Education | 1996 |
| The Martin Vinje Company AS | Information & communication | 2007 |
| Theoseb AS | Financial services | 2007 |
| THG Invest AS | Professional & scientific | 2007 |
| Think Tank AS | Professional & scientific | 1995 |
| Third Coast Business Consulting AS | Information & communication | 2022 |
| Thomas Lyse Fysioterapeut AS | Health & social care | 2015 |
| Thomas N Holding AS | Real estate | 2005 |
| Thomassen International Enterprises Da | | 1994 |
| Thunbolaget AS | Transport & logistics | 1964 |
| Tidi Digital AS | Information & communication | 2025 |
| Til Det Er Tomt AS | Hospitality | 2019 |
| Tiltaket AS | Health & social care | 2024 |
| Timi Holding AS | Wholesale & retail | 2005 |
| Tind Holding AS | Real estate | 2010 |
| Tjæregravshøgda Invest AS | | 2025 |
| Tm-Invest AS | Real estate | 2018 |
| Togreiser AS | Administrative & support | 2017 |
| Tom Bjerke AS | Professional & scientific | 1999 |
| Tom Lundblad AS | Wholesale & retail | 1982 |
| Tomter Invest AS | Financial services | 2005 |
| Tomter Lodge AS | | 2006 |
| Tone Guii-Larsen AS | Professional & scientific | 2023 |
| Tonic Design AS | Professional & scientific | 2003 |
| Topaa AS | Professional & scientific | 2012 |
| Topit Eiendom AS | Real estate | 2019 |
| Torget 1 Drøbak AS | Real estate | 2017 |
| Torget 7 Drøbak AS | Real estate | 2021 |
| Torp Auto AS | Wholesale & retail | 1997 |
| Tour Holding AS | Real estate | 2005 |
| Tre Eker AS | Real estate | 2019 |
| Tre-Tech AS | Construction | 2007 |
| Tre-Tech Holding AS | Construction | 2000 |
| Trendheim AS | Professional & scientific | 2011 |
| Treningskompasset AS | Education | 2024 |
| Trimar Holding AS | Health & social care | 2025 |
| Triniboren AS | Construction | 2005 |