| ST. Croix Hovedgård AS | Real estate | 2016 |
| St.Hansfjellet Eiendom AS | Construction | 2010 |
| St.Hansgt. 1 M&T AS | Real estate | 2005 |
| Staav AS | | 2014 |
| Stabburveien 1 AS | Real estate | 2016 |
| Stabburveien 10 AS | Real estate | 2024 |
| Stabburveien 16 AS | Real estate | 2014 |
| Stabburveien 20 AS | Real estate | 2024 |
| Stabburveien 24 Fredrikstad AS | Real estate | 2021 |
| Stabburveien 6 AS | Real estate | 1997 |
| Start Smart AS | Information & communication | 2018 |
| Stav Mat AS | Manufacturing | 2024 |
| Stavlund AS | Real estate | 2001 |
| Stayonline AS | Information & communication | 2008 |
| Staysman Invest AS | Real estate | 2022 |
| Staysman Live AS | Information & communication | 2021 |
| Steady Home AS | Real estate | 2015 |
| Steeam Company AS | Wholesale & retail | 2012 |
| Steinar Solgaard Holding AS | Wholesale & retail | 2005 |
| Steingrid AS | Real estate | 2000 |
| Steinhaugen AS | Professional & scientific | 2021 |
| Steken Eiendom AS | Real estate | 1997 |
| Stellar Solskjerming AS | Construction | 2022 |
| Stenbryggen AS | Real estate | 2003 |
| Stenman Invest AS | | 2021 |
| Stern Auto Ans | Wholesale & retail | 1997 |
| Stewa AS | Professional & scientific | 2005 |
| STG 5 Bistro AS | Hospitality | 2020 |
| Stille Styrke AS | Education | 2011 |
| Stilmed AS | Health & social care | 2023 |
| Stjernehallen Eiendom AS | Real estate | 2018 |
| Storelva Utvikling AS | Real estate | 2020 |
| Storgata 13 Fredrikstad AS | Real estate | 2008 |
| Storgata 32 Fredrikstad AS | Real estate | 2024 |
| Storgaten 14 AS | Manufacturing | 1934 |
| Storgaten 6 AS | Real estate | 1997 |
| Storgaten 8 Eiendom AS | Real estate | 2005 |
| Stortorvet 1-3 AS | Real estate | 2015 |
| Storveien 81 Eiendom AS | Real estate | 2012 |
| Stramo AS | Construction | 2017 |
| Streken Service Og Vedlikehold AS | Administrative & support | 2020 |
| Stride Norge AS | Administrative & support | 2018 |
| Stua Interiør AS | Wholesale & retail | 1989 |
| Studio 90 Ans | Other services | 1990 |
| Studio Cicignon AS | Hospitality | 2023 |
| Studio Hårfagre AS | Other services | 2011 |
| Studiogeist AS | Professional & scientific | 2017 |
| Studium Actoris AS | Arts & recreation | 2014 |
| Støy Festivalen AS | Arts & recreation | 2026 |
| Sub Fokusgården AS | Hospitality | 2019 |
| Subsea Trenching Services AS | Construction | 2005 |
| Sun-Chris Holding AS | Real estate | 1938 |
| Sunbay AS | Professional & scientific | 2014 |
| Sundt Eiendom AS | Real estate | 2003 |
| Surf Media AS | Professional & scientific | 2023 |
| Sval Festivalen AS | Administrative & support | 2026 |
| Svane Kjøkken Fredrikstad AS | Wholesale & retail | 2021 |
| Svaneveien Eiendom AS | Construction | 2016 |
| Svehan AS | Professional & scientific | 2021 |
| Svein Gressløs Invest AS | Professional & scientific | 2017 |
| Svein Gressløs Kunstformidling AS | Wholesale & retail | 2001 |
| Svela Eiendom AS | Real estate | 1992 |
| Svela Solutions AS | Professional & scientific | 2002 |
| Svela Trailer AS | Wholesale & retail | 2009 |
| Svela Trailertech AS | Administrative & support | 2018 |
| Svelacat AS | Professional & scientific | 2023 |
| Sverre Bergstrøm Eiendom AS | Real estate | 1991 |
| Sverre Bergstrøm Holding AS | Real estate | 2011 |
| Svetre Holding AS | | 2024 |
| Sving Helse AS | Health & social care | 2005 |
| Sydenleiligheter AS | Wholesale & retail | 2011 |
| Sykt Fett AS | Information & communication | 2023 |
| Synergier AS | Professional & scientific | 2017 |
| Synergo AS | Real estate | 1989 |
| Syver Syversen & Sønn AS | Construction | 2003 |
| Syver Syversen & Sønn Eiendom AS | Real estate | 1979 |
| Syversen AS | Wholesale & retail | 1974 |
| Syversen Bygg AS | Construction | 2013 |
| Syversen Group AS | | 2025 |
| Syversen Group Holding AS | Wholesale & retail | 2024 |
| Söderberg & Partners Øst AS | Financial services | 1989 |
| Søco Eiendom AS | Real estate | 2015 |
| Søma Muddring Og Sjøtransport Ans | Transport & logistics | 2002 |
| Søndre Kråkerøy Vann Og Avløpslag SA | Water & waste | 2007 |
| Sørbygg AS | | 2019 |
| Søren Wiese Aktieselskab | Wholesale & retail | 1900 |
| Søstrene Larsen Ans | Wholesale & retail | 1996 |
| T.A.O. AS | Professional & scientific | 2013 |
| T.O.Fjeld AS | Construction | 2013 |
| T.T.Service A/S | Construction | 1987 |
| Ta Anlegg & Sten AS | Construction | 2025 |
| Ta Holding AS | | 2015 |
| Ta to AS | Wholesale & retail | 2010 |
| Takk AS | Hospitality | 2024 |
| Takstco AS | Real estate | 1994 |
| Talb AS | Wholesale & retail | 1999 |
| Tankekraft AS | Education | 2021 |
| Tann I Tiden AS | Health & social care | 2016 |
| Tannlege Anders Samuelsen AS | Health & social care | 2019 |
| Tannlege Boman AS | Health & social care | 2023 |