| Stabburveien 3 AS | Real estate | 2010 |
| Stamsaas AS | Wholesale & retail | 1953 |
| Stamsaas Fritid AS | Wholesale & retail | 2006 |
| Stamsaas Holding AS | Real estate | 2006 |
| Stay Concept AS | Hospitality | 2021 |
| Stay One AS | Hospitality | 2023 |
| Steen & Olsen AS | Construction | 1996 |
| Steinar Klavestad Holding AS | Construction | 2005 |
| Sten Johnsen Restaurantdrift AS | Hospitality | 2015 |
| Stenborg Eiendom AS | Real estate | 2023 |
| Stender Consult AS | Wholesale & retail | 2023 |
| Stender Regnskap AS | Professional & scientific | 2022 |
| Stenerød Gård AS | Real estate | 2018 |
| Stian Martinsen AS | | 2021 |
| Stikom AS | Professional & scientific | 1989 |
| STL Holding AS | | 2023 |
| Storbogen AS | Administrative & support | 2020 |
| Storbyen Legesenter AS | Health & social care | 2000 |
| Storbyen Ur & Gull AS | Wholesale & retail | 2004 |
| Storeper Barnehage AS | Education | 2022 |
| Storgata AS | Real estate | 2024 |
| Storm Elektro Sarpsborg AS | Construction | 2004 |
| Stort Å Holding AS | | 2020 |
| Strandgata 2 Sarpsborg AS | Real estate | 2020 |
| Strongerpeople AS | Administrative & support | 2019 |
| Strømnes Consultants AS | Professional & scientific | 1990 |
| Studio Bloom AS | Wholesale & retail | 2018 |
| Studio Duo Frisør AS | Other services | 2025 |
| Studio Eik AS | Professional & scientific | 2021 |
| Studio Formidable AS | Professional & scientific | 2014 |
| Studio Larsen Arkitektur AS | Professional & scientific | 2013 |
| Stålverkskroken Barnehage AS | Education | 2022 |
| Subclub Da | Information & communication | 2025 |
| Sulland Østfold AS | Wholesale & retail | 1977 |
| Sultan Pizza Grill Ans | Hospitality | 1989 |
| Sunset Boulevard Norge AS | Hospitality | 2023 |
| Supportgutta AS | Information & communication | 2026 |
| Sushi Lille Saigon AS | Hospitality | 2017 |
| Svein Lund Holding AS | Real estate | 2005 |
| Svein Lund Isolering AS | Construction | 2005 |
| Swibb AS | Real estate | 2022 |
| SWR Retail AS | Wholesale & retail | 2025 |
| Sydskogen Barnehage AS | Education | 2022 |
| Sydvold Holding AS | Construction | 2017 |
| Sykkelreparatøren Sarpsborg AS | Other services | 2026 |
| Synsenteret Sarpsborg AS | Wholesale & retail | 2006 |
| Systuen Sarpsborg Ans | Manufacturing | 1997 |
| Syvers Holding AS | | 2026 |
| Skjeberg Investment AS | Manufacturing | 1967 |
| Soundwave Audio ANS | | 1988 |
| Særp Tropez AS | Arts & recreation | 2025 |
| Sætherbakken Forvaltning AS | | 2022 |
| Søgaard Holding AS | Construction | 2024 |
| Søgaard Service AS | Construction | 2024 |
| Sølvberget Invest AS | Real estate | 2014 |
| Sørlie & Westli Ans | Real estate | 1996 |
| Sørlie Bil AS | Wholesale & retail | 2020 |
| Sørlie Billakkering AS | Other services | 1986 |
| Sørlie Bygg AS | Real estate | 2018 |
| Sørlie Gruppen AS | Real estate | 2018 |
| Sørlie Prosjektinnredninger AS | Wholesale & retail | 1995 |
| Sørlie Torget AS | Real estate | 2018 |
| Søtorp Holding AS | | 2020 |
| T Lund Terrasse AS | Real estate | 2025 |
| T M Byggeartikler Da | Wholesale & retail | 1992 |
| Ta Fastigheter AS | Real estate | 2016 |
| Takelund AS | Manufacturing | 2019 |
| Takfornying Øst AS | Construction | 2022 |
| Taktisk AS | Professional & scientific | 2006 |
| Tannlege Frank Wevelstad AS | Health & social care | 2026 |
| Tannlege Patrik Wevelstad AS | Health & social care | 2026 |
| Team TH Bygg Haugen AS | Construction | 2026 |
| Tec Tak AS | Construction | 2012 |
| Tech Safety Engineering AS | Professional & scientific | 2022 |
| Tegneby & Grønnerød Landbruksmegling AS | Real estate | 2018 |
| Tegneby & Grønnerød Landbruksmegling Trøndelag AS | Real estate | 2019 |
| Tekcom Norge AS | Wholesale & retail | 2020 |
| Teknimek AS | Wholesale & retail | 2011 |
| Tenneco Automotive AB | Manufacturing | 1998 |
| TGV Utvikling AS | Professional & scientific | 2021 |
| TGV Utvikling Drift AS | Professional & scientific | 2026 |
| The Easiest Sock in the World AS | Information & communication | 2015 |
| The Force Da | Administrative & support | 2006 |
| Thea Ådalen Holding AS | | 2024 |
| Thelmia Holding AS | | 2024 |
| Themar Holding AS | Real estate | 2011 |
| Thoreby Tak AS | Construction | 2019 |
| Thyst AS | Administrative & support | 2011 |
| Thøgerboats AS | Wholesale & retail | 2007 |
| Tibi Holding AS | Information & communication | 2022 |
| Tibi Media AS | Information & communication | 2022 |
| Tieba Bakeri AS | Manufacturing | 2025 |
| Timit AS | Information & communication | 2019 |
| Timm Eiendom AS | Real estate | 2022 |
| Timm Holding AS | Manufacturing | 2021 |
| Tindlund Park AS | Real estate | 2013 |
| Tinq AS | Information & communication | 2025 |
| Tjurholmens Eiendom | Transport & logistics | 1995 |
| TK Vinduer AS | Wholesale & retail | 2019 |
| Tk&Jk Invest AS | | 2022 |