| SC1ENT Group Norge AS | Professional & scientific | 2022 |
| Scandi Engros AS | Administrative & support | 2019 |
| Scandic Crane Service AS | Administrative & support | 2017 |
| Scandicana AS | Arts & recreation | 2007 |
| Scandsteel AS | Construction | 2023 |
| Sea Extreme Da | Arts & recreation | 2017 |
| Sea Østfold Da | Administrative & support | 2003 |
| Seljevik Veilag SA | Real estate | 2023 |
| Selskapsservice Halden AS | Hospitality | 2003 |
| Semantisys AS | Information & communication | 2023 |
| Sembom Hjem AS | Real estate | 2016 |
| Semotek Norge AS | Professional & scientific | 2026 |
| Sentrumslegene I Halden Da | Health & social care | 2009 |
| Servicealliansen Østfold AS | Administrative & support | 2016 |
| Sesse Holding AS | | 2022 |
| Seven Sisters Holding AS | | 2025 |
| Sibirius AS | Health & social care | 2016 |
| Sifab Interiør AB Nuf | Construction | 1995 |
| Sig Eiendom AS | Real estate | 2005 |
| Sig Gruppen AS | Real estate | 2005 |
| Signebøenfjellet Veilag SA | Real estate | 2023 |
| Signed Sports AS | Wholesale & retail | 2026 |
| Sihb Holding AS | | 2025 |
| Silhouette Nordic Nuf | Wholesale & retail | 2014 |
| Simer AS | Professional & scientific | 2010 |
| Sindelika Holding AS | Information & communication | 2021 |
| Sininvest AS | Professional & scientific | 2019 |
| Sirius Event AS | Arts & recreation | 2022 |
| Siste Reis AS | Hospitality | 2018 |
| Sito Eiendom 1 AS | Real estate | 2011 |
| Sito Holding AS | Real estate | 2021 |
| Sivertsen Trading AS | Wholesale & retail | 2013 |
| SJB Kapital AS | | 2021 |
| Sjevalier Holding AS | Professional & scientific | 2020 |
| Skandimarmor AS | Wholesale & retail | 2019 |
| Skandinavisk Eiendomsutvikling AS | Construction | 1996 |
| Skansenlia Bolig AS | Real estate | 2015 |
| Skar Eiendom AS | Real estate | 1999 |
| Skilt & Fasadehjelpen AS | Professional & scientific | 2004 |
| Skippergata 2-4 AS | Real estate | 2005 |
| Skippergata Institutt Ans | Health & social care | 2001 |
| Skippergata Institutt AS | Health & social care | 2013 |
| Skjelin AS | Construction | 2017 |
| Skjelin Eiendom AS | Real estate | 2021 |
| Skjelin Holding AS | Real estate | 2012 |
| Skogheim Holding AS | Real estate | 2005 |
| Skogheim Og Torp Malerservice Ans | Construction | 2005 |
| Skogkanten Dyr & Naturbarnehage AS | Education | 2008 |
| Skogli Eiendom AS | Real estate | 1999 |
| Skoland Elektro AS | Construction | 2026 |
| Skram Maskin AS | Construction | 2018 |
| Skuff På Skuff Maskin AS | Administrative & support | 2024 |
| Skyen Holding AS | Professional & scientific | 2022 |
| Skyen Regnskap AS | Professional & scientific | 2022 |
| Slang Holding AS | | 2021 |
| Slitu Nærings Og Handelspark AS | Real estate | 2019 |
| Smaalensbanen Eiendomsinvest AS | Real estate | 2009 |
| Smaalensbanen Invest AS | Real estate | 2012 |
| Smart Innovation Holding AS | Professional & scientific | 2022 |
| Smart Innovation Norway AS | Professional & scientific | 2003 |
| Smart Innovation Venture AS | Professional & scientific | 2024 |
| Smartfordelt AS | Education | 2026 |
| Smolt Eiendom AS | Real estate | 2017 |
| Småkryp Da | Wholesale & retail | 2000 |
| Snadder AS | Wholesale & retail | 2010 |
| Snø Miljøvennlig Frisør AS | Other services | 2000 |
| Social Division AS | Health & social care | 2019 |
| Sodatech AS | Wholesale & retail | 2018 |
| Sofienlund Løvtre AS | Manufacturing | 2024 |
| Solar Solutions AS | Wholesale & retail | 2022 |
| Solar Village AS | Professional & scientific | 2013 |
| Solbakken Naturbarnehage AS | Education | 2022 |
| Solheim Service AS | Manufacturing | 2019 |
| Sollihøgda Bolig AS | Real estate | 2017 |
| Solsidan Eiendom AS | Real estate | 2026 |
| Solåsen Bygg AS | Real estate | 2017 |
| Some Design AS | Wholesale & retail | 2023 |
| Someduo Da | Professional & scientific | 2022 |
| Sonaab AS | Professional & scientific | 2020 |
| Soror AS | Real estate | 2005 |
| Soul-Spa AS | Other services | 2023 |
| Spesialtransport AS | Construction | 2018 |
| Spinnvill Tech AS | Arts & recreation | 2008 |
| Sponvika Åsen AS | Real estate | 2020 |
| Sponvikene AS | Real estate | 2011 |
| Sport Senteret AS | Wholesale & retail | 1993 |
| Sportsdeler AS | Other services | 2024 |
| Sportsfood AS | Wholesale & retail | 2021 |
| Squarehead Holding AS | Financial services | 2005 |
| Stadionhuset AS | Real estate | 2010 |
| Stall KS AS | Real estate | 2021 |
| Stall LS AS | Arts & recreation | 2025 |
| Stanseformfabrikken AS | Manufacturing | 1994 |
| Starcut Dame & Herre Frisør AS | Other services | 2020 |
| Staxvold Holding AS | Education | 2011 |
| STB Holding AS | Real estate | 2019 |
| Steadikameratene AS | Information & communication | 2006 |
| Stefan Knutsson Transport AB | Transport & logistics | 2008 |
| Stein & K E Antikk Og Brukt Ans | | 1989 |
| Steinservice Østfold AS | Manufacturing | 2010 |