| Olav Haugen Transport AS | Transport & logistics | 2003 |
| Omnisoft AS | Information & communication | 1994 |
| Onion Holding AS | | 2024 |
| Opsahlveien 3 AS | Real estate | 2019 |
| Orca Holding AS | | 2021 |
| Ostara Naturals AS | Wholesale & retail | 2014 |
| Oststar AS | | 2025 |
| Oveni AS | Real estate | 2021 |
| P Larsson Stensätteri Patrik Larsson | Construction | 2000 |
| P-O Lundbergs Svetsposition AB | Manufacturing | 2008 |
| P3 Elektro AS | Construction | 2021 |
| Panda Restaurant Mysen AS | Hospitality | 2023 |
| Panorama Di Roma AS | Hospitality | 2025 |
| Peaas Invest AS | Administrative & support | 2022 |
| Pedersen Anlegg-Service AS | Manufacturing | 2020 |
| Pefo Eiendom AS | Real estate | 2011 |
| Pennestrøket 13 AS | Real estate | 2010 |
| Per's Eiendom AS | Real estate | 2005 |
| Peta AS | Administrative & support | 2001 |
| Phoenix Transport AS | Transport & logistics | 2020 |
| Pixel Motorsport AS | Wholesale & retail | 2016 |
| PK Kapital AS | Real estate | 2015 |
| PK Prosjektutvikling AS | Real estate | 2025 |
| Pristine Vent AS | Administrative & support | 2025 |
| Produksjonsveien 3 AS | Real estate | 2025 |
| Profvent AS | Construction | 2022 |
| Proletary Games AS | Information & communication | 2021 |
| Protokoll AS | Professional & scientific | 1997 |
| PX Design AS | Other services | 2015 |
| Ramatec AS | Real estate | 1980 |
| Ramberg Bil AS | Wholesale & retail | 2010 |
| Ramstad Lastebilservice AS | Other services | 1991 |
| Ramstadløkka 1 AS | Real estate | 2025 |
| Ramstadløkka 3 AS | Manufacturing | 2023 |
| Ramstadløkka 4 Og 6 AS | Real estate | 2023 |
| Ramstadløkka 6 AS | Real estate | 2021 |
| Ramstadløkka Eiendom AS | Real estate | 2008 |
| Ramstadtoppen 1 AS | Real estate | 2025 |
| Ramstadtoppen 2 AS | Real estate | 2025 |
| Ramstadtoppen AS | Real estate | 2021 |
| Ramstadveien 2 Eiendom AS | Wholesale & retail | 2017 |
| Ramstadveien 7 AS | Real estate | 2005 |
| Rett Vest Mysen Ans | Administrative & support | 2002 |
| RG Internetthandel Hafstad & Karlsen Da | Wholesale & retail | 2000 |
| Rhino Linings Norway AS | Wholesale & retail | 2008 |
| Rin Regnskap AS | Professional & scientific | 1998 |
| Robin M. AS | Construction | 2006 |
| Rod Bianco Gallery AS | Wholesale & retail | 2004 |
| Roger AS | Construction | 2006 |
| Rollover AS | Manufacturing | 2000 |
| RS Tømrerservice AS | Construction | 2015 |
| S-Invest AS | Construction | 2005 |
| Saa Football Management AS | Arts & recreation | 2020 |
| Sagtomta Utvikling Mysen AS | | 2015 |
| Sander AS | Real estate | 2021 |
| Sanne AS | Health & social care | 2016 |
| SE Bygg I Värmland AB | Construction | 2000 |
| Seim Trær Og Planter AS | Agriculture & fishing | 1965 |
| Sentrum Blomster Mysen AS | Wholesale & retail | 2014 |
| Signare AS | Professional & scientific | 2003 |
| Signaturadesign AS | Manufacturing | 2026 |
| Sing Anywhere AS | Information & communication | 2022 |
| Siv Ing Helge Andreassen AS | Professional & scientific | 2000 |
| SK Gjerstad Transport AS | Transport & logistics | 2021 |
| Skarpsno Eiendom AS | Real estate | 2014 |
| Skau Eiendom AS | Real estate | 2023 |
| Skofterud AS | Real estate | 2005 |
| Skogex AS | Agriculture & fishing | 2016 |
| Skraaperud Holding AS | Real estate | 2019 |
| Skrikerud Søndre Da | Agriculture & fishing | 2020 |
| Slitu Kolonial AS | Wholesale & retail | 2025 |
| Smaalenene Bedriftshelsetjeneste AS | Health & social care | 2019 |
| Smaalenene Begravelsesbyrå AS | Other services | 2024 |
| Smaalenene Konsult AS | Professional & scientific | 2007 |
| Smaalenene Revisjon AS | Professional & scientific | 2006 |
| Smedgaten 4 AS | Real estate | 2005 |
| Smedgaten 9 AS | Real estate | 2024 |
| Smedgaten Kontormøbler AS | Real estate | 1986 |
| Smedgt 1 AS | Real estate | 1998 |
| Smestad Eiendom AS | Real estate | 2006 |
| SML Holding AS | Wholesale & retail | 2005 |
| Smultringen AS | Wholesale & retail | 2020 |
| Smådahl AS | Construction | 1999 |
| Smådahl Eduardsen AS | Construction | 2021 |
| Snacbaren Mysen AS | Hospitality | 2020 |
| Snack House Mysen AS | Hospitality | 2026 |
| Solbjørgs Økonomi & Regnskap AS | Professional & scientific | 2015 |
| Sollihagen Bygg AS | Construction | 2014 |
| Spekemat 1 AS | Wholesale & retail | 2010 |
| Spinneridalen Eiendom AS | Real estate | 2000 |
| Spinnin Wheel AS | Other services | 1991 |
| Spitzenklasse AS | Financial services | 2011 |
| Sr-Service Woodtrade AS | Wholesale & retail | 2011 |
| Starbreather Production AS | Construction | 2015 |
| Stein Garmann Holding AS | | 2025 |
| Stemmedalen AS | Construction | 2010 |
| Stian Skau Transport AS | Transport & logistics | 2013 |
| Stili Holding AS | Real estate | 2020 |
| Stillesby Bygg AS | Construction | 2019 |
| Stomatek Nuf | Manufacturing | 2005 |