| Nielsen Takst Og Energirådgiver AS | Real estate | 2024 |
| NMC Norge AS | Manufacturing | 1981 |
| Nor-Gass AS | Administrative & support | 2010 |
| Noramar AS | | 2021 |
| Norbygg AS | Construction | 1979 |
| Norbygg Holding AS | Construction | 2023 |
| Norcore Invest AS | | 2026 |
| Nordic Hemp AS | Professional & scientific | 2021 |
| Norkolli AS | Transport & logistics | 2018 |
| Norplan AS | | 2023 |
| Norrøn Bygg AS | Real estate | 2006 |
| Norsk Arbeidshelse AS | Health & social care | 2015 |
| Nory AS | Wholesale & retail | 2019 |
| Nova Holding AS | Manufacturing | 2005 |
| Nuvio AS | Professional & scientific | 2021 |
| Nygaardsgata 39 Holding AS | Real estate | 2017 |
| O.L. Holding AS | Financial services | 2005 |
| Ohnstad Holding AS | Health & social care | 2022 |
| Oliva Park AS | Administrative & support | 2018 |
| Olseng Holding AS | Wholesale & retail | 2018 |
| One Solutions AS | Manufacturing | 2019 |
| Onibilliare Holding AS | | 2013 |
| Osto Holding AS | | 2025 |
| Ovre Invest AS | | 2012 |
| Pace Fitness Group AS | Arts & recreation | 2026 |
| Pallesentralen Avd Østfold AS | Wholesale & retail | 2026 |
| Palp Holding AS | | 2020 |
| Pappen Utvikling AS | Real estate | 2020 |
| Park & Anlegg AS | Construction | 2000 |
| Pawel Iskra | Construction | 2007 |
| PB Bolig AS | Real estate | 2015 |
| PB Eiendomsinvest AS | Real estate | 2016 |
| PCG Holding AS | Construction | 2023 |
| Persi AS | Administrative & support | 2010 |
| Pesi Holding AS | | 2025 |
| Piotr Haniszewski | Construction | 2007 |
| Piotr Klejman Bygningshåndverker | Construction | 2004 |
| Piotr Kowalski Bud | Construction | 2007 |
| Pol Betong AS | Construction | 2011 |
| Polan AS | Construction | 2022 |
| Probygg AS | Construction | 2014 |
| Profesjonell Mekanikk AS | Manufacturing | 2024 |
| Psykologhjelp AS | Health & social care | 2017 |
| Psykologspesialist Richard Hamström Nuf | Health & social care | 2023 |
| PT Rørleggerservice AS | Construction | 2010 |
| Pål Magnus Holding AS | | 2023 |
| Pædde.Com AS | Wholesale & retail | 2023 |
| Quality Hotel Og Badeland Sarpsborg AS | Hospitality | 1999 |
| Quality Transport AS | Transport & logistics | 2020 |
| R Agentur AS | Wholesale & retail | 2020 |
| R. Eiendomsforvaltning AS | Real estate | 2020 |
| Rikke Bering AS | Financial services | 2017 |
| Rikter Svendsen Holding AS | | 2024 |
| Ringtun Eiendom AS | Real estate | 2024 |
| Ringtun Gruppen AS | Professional & scientific | 2009 |
| Ringtunveien 9 Eiendom AS | Construction | 2014 |
| Robert Chmielewski Robi | Construction | 2007 |
| Robert Nowarkiewicz Norwarkiewicz | Construction | 2007 |
| Robert Wieczorek Rob | Construction | 2007 |
| Rosenvinge Park Felt 2A AS | Real estate | 2017 |
| Rosenvinge Park Felt 2B AS | Real estate | 2018 |
| Runar Jørgensen AS | Wholesale & retail | 2007 |
| Ryens Rørservice AS | Construction | 2017 |
| Rådmann Siras Vei 8 AS | Real estate | 2025 |
| Røed Data Og Design AS | Information & communication | 2024 |
| Rørcompaniet - Service AS | Construction | 2019 |
| Rørcompaniet AS | Construction | 2006 |
| S. Aarum Holding AS | | 2024 |
| S.T Holding AS | | 2025 |
| Sagatunveien 1-3 AS | Real estate | 2001 |
| Sama Invest AS | Real estate | 2014 |
| Sarpsborg Bil Og Transport AS | Transport & logistics | 2016 |
| Sarpsborg Byggeteknikk & Arkitektur | Real estate | 2016 |
| Sarpsborg Elektro AS | Construction | 2018 |
| Sarpsborg Fotball Invest AS | Arts & recreation | 2001 |
| Sarpsborg Kiropraktorklinikk AS | Health & social care | 2016 |
| Sarpsborg Spesialisttjenester AS | Health & social care | 2024 |
| Schjøllert Invest AS | Financial services | 2005 |
| Semerk AS | Wholesale & retail | 2019 |
| Sensor Technology AS | Manufacturing | 2004 |
| Shain IT AS | Administrative & support | 2025 |
| Shape Invest AS | | 2019 |
| Siksjø & Jakobsen Holding AS | Real estate | 2007 |
| Silva Norway Nuf | Information & communication | 2013 |
| Sindre Borgli AS | Education | 2020 |
| Siteforge AS | Information & communication | 2025 |
| Skard Invest AS | Real estate | 2020 |
| Skarp Net Ans | Construction | 2000 |
| Skjelle Invest AS | Construction | 2005 |
| Skjervengen Invest AS | | 2021 |
| Skolt Entreprenør Holding AS | Construction | 2000 |
| Skyscope AS | Professional & scientific | 2025 |
| Slawomir Grzenkowicz Slaw | Construction | 2007 |
| SM Bygg Og Eiendom AS | Real estate | 2017 |
| Smartis AS | Wholesale & retail | 2019 |
| SML Lighting AS | Wholesale & retail | 1988 |
| SP Engineering AS | Professional & scientific | 2015 |
| Sparebank 1 Regnskapshuset Østfold Akershus AS | Professional & scientific | 1993 |
| SR Forsikring AS | Financial services | 2017 |
| SRT Holding AS | Health & social care | 2016 |