| Sarpsborg Treningssenter AS | Arts & recreation | 2025 |
| Sarpsborg Øyelegesenter Da | Health & social care | 2002 |
| SARPSBORG24 AS | Information & communication | 2015 |
| Sarpsfoss Limited Nuf | Energy | 1995 |
| SAS Auto AS | Wholesale & retail | 2026 |
| SAS Drift AS | Wholesale & retail | 2023 |
| SAS Investment AS | Professional & scientific | 2021 |
| Savior AS | Wholesale & retail | 2013 |
| SB Bolig AS | Real estate | 2020 |
| SB Entreprenør AS | Construction | 2014 |
| Scandic Byggservice AS | Construction | 2021 |
| Schille Turid Tannlege AS | Health & social care | 1996 |
| Schur International | Wholesale & retail | 2006 |
| Sefa Eiendom AS | Real estate | 2012 |
| Sefa Holding AS | Real estate | 2012 |
| Selman Eiendom AS | Real estate | 2011 |
| Selskapsdekorering AS | Professional & scientific | 2021 |
| Senior Inspection AS | Professional & scientific | 2017 |
| Senterdekk Borg AS | Other services | 2018 |
| Sentrum Legesenter Da | Health & social care | 2001 |
| Sentrum Profiltrykk AS | Manufacturing | 2021 |
| Servicesenteret Østfold AS | Other services | 1981 |
| SG Borg AS | Real estate | 2005 |
| SG Kommunikasjon AS | Information & communication | 2017 |
| SG Regnskap AS | Professional & scientific | 2022 |
| SG Torget AS | Real estate | 2015 |
| SH Naprapati & Coaching AS | Health & social care | 2026 |
| Ship Shape Norge AS | Wholesale & retail | 2016 |
| Shipping Partner Sarpsborg Holding AS | Real estate | 1994 |
| Shna AS | Other services | 2013 |
| Sigve Ådalen Holding AS | | 2024 |
| Sikte AI AS | Professional & scientific | 2026 |
| Silkoset Group AS | | 2025 |
| Silverpoppeln Holding AS | | 2025 |
| Simensen Eiendom AS | Real estate | 1975 |
| Singh Mat AS | Hospitality | 2020 |
| Sirius AS | Wholesale & retail | 1998 |
| Sivilingeniør Per Kristian Ubøe AS | Education | 1987 |
| Sjusjøen Invest AS | Real estate | 2009 |
| Skala Regnskap AS | Professional & scientific | 2025 |
| Skaug Barnehage AS | Education | 2022 |
| Skeidar Sarpsborg AS | Wholesale & retail | 2000 |
| Skinnarmo Consult AS | | 2021 |
| Skjoldensvei 9 AS | Real estate | 2020 |
| Skofiks AS | Other services | 2016 |
| Skogr Gruppen AS | Real estate | 2021 |
| Skogro Barnehage AS | Education | 2003 |
| Skribent-Kompaniet Da | Arts & recreation | 2017 |
| Skrifvars Entreprenad Nuf | Agriculture & fishing | 2016 |
| Skråtorp Utvikling AS | Real estate | 2016 |
| Skule Reiersen AS | Financial services | 2005 |
| Sky Regnskap AS | Professional & scientific | 2021 |
| Skåland Maskin AS | Construction | 2021 |
| Skåland Utleie AS | Administrative & support | 2022 |
| Skår Andreassen Holding AS | Construction | 2022 |
| Smaalenene Handel Ans | Education | 2013 |
| Smart Vask AS | Administrative & support | 2019 |
| Smeby Service AS | Construction | 2024 |
| SMW Holding AS | Real estate | 2022 |
| SN Invest AS | | 2018 |
| Snarr AS | Information & communication | 2026 |
| Snarveien Fus Barnehage AS | Education | 2018 |
| Snekkerstubakken 24 AS | Wholesale & retail | 2019 |
| Snuen AS | | 2026 |
| Sobbl Boliger AS | Real estate | 2004 |
| Sobbl Eiendom AS | Real estate | 1998 |
| Sogn Øyelegesenter AS | Health & social care | 2025 |
| Soland Invest AS | Construction | 2005 |
| Solathom Holding AS | Wholesale & retail | 2024 |
| Solbakkeparken Barnehage AS | Education | 2022 |
| Solbyen Bilpleie AS | Other services | 2023 |
| Solbyen Eiendom AS | Real estate | 2019 |
| Solbyen Maki House AS | Hospitality | 2023 |
| Solbyen Utvikling AS | Real estate | 2008 |
| Solhøi Revisjon AS | Professional & scientific | 1989 |
| Solid Computers Ans | Information & communication | 1999 |
| Solsikken Familiebarnehage Da | Education | 1997 |
| Sondre Lien Holding AS | | 2022 |
| Song Shan AS | Real estate | 2012 |
| Sovinox AS | Manufacturing | 1999 |
| Sparta Hockeyshop AS | Wholesale & retail | 2007 |
| Spartakiosken AS | Wholesale & retail | 2020 |
| Spartaklinikken Da | Health & social care | 2009 |
| Speak Publishing Da | Arts & recreation | 2001 |
| Sport Esset AS | Wholesale & retail | 2021 |
| Sport Import AS | Wholesale & retail | 2020 |
| Sporter AS | Wholesale & retail | 2020 |
| Sports-Medisinske Produkter Norge AS | Arts & recreation | 1985 |
| Spretten Idrettsbarnehage AS | Education | 1999 |
| Spring Agency AS | Professional & scientific | 2022 |
| Spydevold Innvest AS | Financial services | 2020 |
| SST Marine AS | Transport & logistics | 2017 |
| ST Marie Gate 79 AS | Real estate | 2005 |
| ST. Marie Gate 50 AS | Real estate | 2007 |
| ST. Marie GT 107 AS | Real estate | 2015 |
| ST. Marie GT. 86 AS | Real estate | 2005 |
| ST. Mariegate 53 AS | Professional & scientific | 2015 |
| ST. Mariesgt. 109 AS | Real estate | 2012 |
| ST. Olav Trafikkskole AS | Education | 2015 |
| ST1A AS | Real estate | 2021 |