| Slottsbrogruppen AS | Professional & scientific | 2010 |
| SM Prosjekt AS | Construction | 2026 |
| Smak Av Porsgrunn AS | Hospitality | 2023 |
| Smartlåst AS | Professional & scientific | 2026 |
| Smartout AS | Information & communication | 2022 |
| Smartsafe Norge AS | Wholesale & retail | 2025 |
| SMH Holding AS | Financial services | 2005 |
| Smietangen Utbygging AS | Real estate | 2016 |
| Smådyrklinikken AS | Professional & scientific | 2021 |
| Snorre Kongerød AS | | 2024 |
| So Capital AS | | 2021 |
| Sol & Måne Invest AS | Professional & scientific | 2022 |
| Solaastunet AS | Information & communication | 1992 |
| Soland Engros Ans | Wholesale & retail | 1991 |
| Solbakken Utvikling AS | Real estate | 2025 |
| Solbakkmoen Utvikling AS | Real estate | 2022 |
| Solenergi Gruppen AS | | 2023 |
| Solheim Utbygging AS | Real estate | 2022 |
| Solkiosken Dikkon Ans | Wholesale & retail | 1989 |
| Solkysten Holding AS | Real estate | 2020 |
| Solkysten Utvikling AS | Real estate | 2022 |
| Sollinvest AS | | 2026 |
| Solra AS | Energy | 2023 |
| Solstad Eiendom AS | Real estate | 1988 |
| Solstad Holding AS | | 2022 |
| Solstad Transport AS | Transport & logistics | 1988 |
| Solstad Trykk AS | Real estate | 1989 |
| Solum Vektstasjon AS | Real estate | 2021 |
| Solvang Eiendom AS | Real estate | 1980 |
| Solvang Revisjon AS | Professional & scientific | 2005 |
| Solvi Invest AS | | 2021 |
| Som Eiendom AS | Real estate | 1957 |
| Sommartider AS | Hospitality | 2022 |
| Sonja.No AS | Information & communication | 2023 |
| Sonton Teknologi AS | Information & communication | 1996 |
| Sopeservice Da | Administrative & support | 1998 |
| Sortedal Holding AS | | 2025 |
| Sot Down Town AS | Hospitality | 2021 |
| Soulshaker - Last Man Standing AS | Hospitality | 2000 |
| Sparebankgården AS | Real estate | 2006 |
| Spire & Gro Barnehagene AS | Education | 2016 |
| Spire & Gro Liane Barnehage AS | Education | 2020 |
| Spire & Gro Melkeveien Barnehage AS | Education | 2020 |
| Spire & Gro Rypevegen Barnehage AS | Education | 2019 |
| Spire & Gro Skogtoppen Barnehage AS | Education | 2020 |
| SPK Holding AS | | 2025 |
| Spon AS | Construction | 2016 |
| Sport 1 Porsgrunn AS | Wholesale & retail | 2019 |
| Sports Accounting AS | Professional & scientific | 2020 |
| Sportsjentene AS | Arts & recreation | 2018 |
| Sprecks AS | | 2019 |
| Sprek Fritid Porsgrunn AS | Arts & recreation | 2019 |
| Ssi AS | Manufacturing | 2005 |
| SSP Motorcenter AS | Other services | 2019 |
| ST Byggservice AS | Construction | 2010 |
| Stabil Eiendom AS | Construction | 1984 |
| Stabil Holding AS | Construction | 2012 |
| Stabil Varme Service AS | Construction | 2012 |
| Stall Am AS | Arts & recreation | 2017 |
| Stall Elvebredden AS | Arts & recreation | 2016 |
| Stall Vestsyn Da | Arts & recreation | 2004 |
| Stangsgate 1 AS | Real estate | 2011 |
| Star Equipment AS | Real estate | 2020 |
| Stardust Holding AS | | 2021 |
| Stasjonsvegen Utvikling AS | Real estate | 2023 |
| Stathelle Legesenter Eiendom AS | Real estate | 2014 |
| Stauper Environment AS | Professional & scientific | 2022 |
| Stauper Water Technologies AS | Professional & scientific | 2014 |
| Stavern Taksering AS | Real estate | 1989 |
| Steady Catch AS | Professional & scientific | 2021 |
| Steinar Granengs Bilverksted AS | Other services | 1996 |
| Steinar Kaalstad Invest AS | | 2023 |
| Stelans AS | Arts & recreation | 2023 |
| Stellata AS | Arts & recreation | 2008 |
| Stena Confidential AS | Administrative & support | 2020 |
| Stena Recycling AS | Water & waste | 2001 |
| Stena Recycling Decom AS | Water & waste | 2017 |
| Stenberg Eiendomsinvest AS | Real estate | 2015 |
| Stengaarden AS | Education | 2016 |
| Stenseth Tre & Hage AS | Administrative & support | 2016 |
| Stho Holding AS | Health & social care | 2019 |
| Stoa Bolig AS | Real estate | 2007 |
| Stoa Boligutvikling AS | Real estate | 2022 |
| Stockmand AS | Hospitality | 2013 |
| Stomperudveien Utbygging AS | Real estate | 2020 |
| Stone Computing AS | Information & communication | 1999 |
| Stonehome Invest AS | Wholesale & retail | 2003 |
| Stordalen Invest AS | | 2015 |
| Storefjell Holding AS | Construction | 2018 |
| Storg 79 AS | Real estate | 1993 |
| Storgata 101 AS | Real estate | 2018 |
| Storgata 102 AS | Real estate | 2026 |
| Storgata 106 AS | Real estate | 2003 |
| Storgata 107 AS | Real estate | 2018 |
| Storgata 112 AS | Real estate | 2018 |
| Storgata 118 AS | Real estate | 2011 |
| Storgata 133 AS | Real estate | 2015 |
| Storgata 135 AS | Real estate | 2012 |
| Storgata 141 AS | Real estate | 2007 |
| Storgata 89 AS | Real estate | 2024 |