| Seidenweg AS | Financial services | 2013 |
| Seil Invest AS | | 2021 |
| Seil Med Larsen Riggverksted AS | Manufacturing | 2026 |
| Seivall Panorama AS | Real estate | 2022 |
| Seltor AS | Construction | 1971 |
| Seltor Bolig AS | Real estate | 2009 |
| Seltor Bolig Gulsetvegen AS | Real estate | 2022 |
| Seltor Bolig Klosterskogen AS | Construction | 2020 |
| Seltor Bolig Nittedal AS | Real estate | 2018 |
| Seltor Bolig Rykkinn AS | Construction | 2021 |
| Seltor Bolig Strømdal AS | Construction | 2020 |
| Seltor Bolig Strømdalsgrenda AS | Real estate | 2021 |
| Seltor Bolig Tønsberg 1 AS | Real estate | 2018 |
| Seltor Bolig Ulefossvegen AS | Real estate | 2021 |
| Seltor Gruppen AS | Construction | 2008 |
| Sem Utvikling AS | Real estate | 2017 |
| Semsa AS | Real estate | 2018 |
| Senfi Norway AS | Professional & scientific | 2012 |
| Sengehesten AS | Manufacturing | 2022 |
| Senter Eiendom AS | Real estate | 2013 |
| Senter for Maritim Medisin AS | | 2010 |
| Sentrum Tannklinikk Porsgrunn AS | Health & social care | 2022 |
| Seram Coatings AS | Manufacturing | 2014 |
| Servie AS | Professional & scientific | 1991 |
| Servie Eiendom AS | Real estate | 2001 |
| Sesa Consulting AS | Health & social care | 2012 |
| Set Linings International S. a. | Construction | 2009 |
| SH Beauty & Sykepleiertjenester AS | Health & social care | 2023 |
| Shadow IT AS | Information & communication | 2021 |
| SHD AS | Professional & scientific | 2013 |
| Shold AS | Professional & scientific | 2016 |
| Signature Auto AS | Wholesale & retail | 2025 |
| Sikt Utvikling AS | Real estate | 2022 |
| Silverwater AS | Professional & scientific | 2011 |
| Simi Invest AS | Information & communication | 2026 |
| Simonsen Kiropraktikk AS | Health & social care | 2023 |
| Simpla AS | Information & communication | 2025 |
| Simplixity AS | Energy | 2020 |
| Sintel AS | Professional & scientific | 2005 |
| Siram AS | Professional & scientific | 2008 |
| Sirius Familiebarnehage AS | Education | 2012 |
| Sirius Invest AS | Financial services | 2010 |
| Sitas Isolasjon AS | Construction | 2016 |
| Siv. Ing. Hans Narvestad AS | Professional & scientific | 2024 |
| Sivak AS | Administrative & support | 2004 |
| Sivan Frisør AS | Other services | 2016 |
| Sivilingeniør Geir Moe AS | Professional & scientific | 2020 |
| Siviløkonom Knut H Pedersen AS | Professional & scientific | 1987 |
| Sixtens-Holding AS | | 2025 |
| SJB Eiendom AS | Real estate | 2007 |
| Sjøglo AS | Administrative & support | 2025 |
| Sjøstrand Eiendom Ans | Real estate | 2006 |
| Sjøstrøms AS | Construction | 2012 |
| Sjøviken Park AS | Real estate | 2020 |
| SK Invest Ltd Nuf | Professional & scientific | 2013 |
| Skagerak Bio AS | | 2025 |
| Skagerak Elektro AS | Construction | 2014 |
| Skagerak Energi AS | Energy | 1998 |
| Skagerak Energipartner AS | Energy | 2019 |
| Skagerak Energitjenester AS | Energy | 2022 |
| Skagerak Hydrogen AS | Wholesale & retail | 2023 |
| Skagerak Kraft AS | Energy | 1997 |
| Skagerak Mobil Energi AS | Professional & scientific | 2024 |
| Skagerak Utvikling AS | Professional & scientific | 2023 |
| Skagerak Varme AS | Energy | 2005 |
| Skagerrak Eiendomsmegling AS | Real estate | 2024 |
| Skagerrak Sparebank | Financial services | 1849 |
| Skarding Invest AS | | 2021 |
| Skarphedinsveg 1 Eiendom AS | Real estate | 2024 |
| Ske Invest AS | Real estate | 2015 |
| SKH Elektro AS | Professional & scientific | 2022 |
| Skiebe Holding AS | Financial services | 2005 |
| Skien Bobilhotell AS | Real estate | 2021 |
| Skien Brygge Utvikling AS | Real estate | 2020 |
| Skien Næringsfond AS | Public administration | 1982 |
| Skien Sbbl Utleie AS | Real estate | 2023 |
| Skippergata Eiendom AS | Real estate | 1996 |
| Skippergata Holding AS | Real estate | 1988 |
| Skjalg Fysikalske AS | Health & social care | 2015 |
| Skjelsvik Thaifood Takeaway AS | Hospitality | 2025 |
| Skjæveland & Vatne Holding AS | Construction | 2006 |
| Skoe Holding AS | | 2009 |
| Skoghaug Holding AS | | 2005 |
| Skogtoppen 2 AS | Education | 2011 |
| Skolegata 2 Porsgrunn AS | Real estate | 2022 |
| Skolegata 2B AS | Real estate | 2015 |
| Skolegata Invest AS | Real estate | 2010 |
| Skolegården Eiendom AS | Real estate | 1998 |
| Skomvær Holding AS | Real estate | 2016 |
| Skomvær Næring AS | Real estate | 2018 |
| Skoppum Næring AS | Real estate | 2024 |
| SKP Eiendom AS | Real estate | 2017 |
| Skrapeklev Areal AS | Real estate | 2014 |
| Skrapeklev Barnehage SA | Education | 1988 |
| Skriverveien 2-4 AS | Real estate | 2016 |
| Skrukkerødlia Utbygging AS | Real estate | 2021 |
| Skui Invest AS | | 2019 |
| SL Hercules AS | Administrative & support | 2025 |
| SL1 Holding AS | Professional & scientific | 2018 |
| Slevollen Eiendom AS | Real estate | 2013 |