| Porsgrunn Mek AS | Real estate | 1999 |
| Porsgrunn Mek Holding AS | Professional & scientific | 2022 |
| Porsgrunn Min by AS | Professional & scientific | 1996 |
| Porsgrunn Næringspark AS | Real estate | 2010 |
| Porsgrunn Næringspark Holding AS | Real estate | 2022 |
| Porsgrunn Pizza & Grill AS | Hospitality | 2019 |
| Porsgrunn Plastikkirurgi AS | Health & social care | 2013 |
| Porsgrunn Regnskap AS | Professional & scientific | 2024 |
| Porsgrunn Retail AS | Wholesale & retail | 2019 |
| Porsgrunn Rørleggerforretning AS | Construction | 1987 |
| Porsgrunn Shipping AS | Real estate | 2003 |
| Porsgrunn Sushi House AS | | 2026 |
| Porsgrunn Taxi AS | Transport & logistics | 2022 |
| Porsgrunn Utvikling AS | Real estate | 2009 |
| Porsgrunn Øyeklinikk AS | Health & social care | 2018 |
| Porsgrunns Dagblad AS | Information & communication | 1974 |
| Porsgrunnsgynekologene AS | Health & social care | 2020 |
| Porsgrunnsportalen AS | Real estate | 2009 |
| Porsgrunnsveien 346 AS | Real estate | 2008 |
| Port Flow AS | Transport & logistics | 2025 |
| Posos Holding AS | Financial services | 2017 |
| Poulsen Invest AS | Real estate | 2007 |
| Powell AS | Construction | 2017 |
| Powerage Da | Arts & recreation | 2018 |
| Powershop AS | Wholesale & retail | 2022 |
| PPM Prosjekt Porsgrunn AS | Professional & scientific | 2025 |
| Preinvest AS | Real estate | 2005 |
| Prestegårdshagene SA | Agriculture & fishing | 2013 |
| Prochect AS | Information & communication | 2025 |
| Produksjon Senteret AS | Professional & scientific | 2018 |
| Proff Bygg & Vedlikehold AS | Construction | 2023 |
| Profil Reklame AS | Manufacturing | 1993 |
| Proftech AS | Professional & scientific | 2026 |
| Progressio Brage Finans AS | Real estate | 2005 |
| Project 5077 AS | | 2025 |
| Project Invest AS | Professional & scientific | 2000 |
| Project NXT AS | Information & communication | 2024 |
| Prok AS | Professional & scientific | 2012 |
| Properti AS | Information & communication | 2022 |
| Proretur AS | Water & waste | 2022 |
| Prospective AS | Real estate | 2016 |
| Prospective Utvikling AS | Real estate | 2017 |
| Protesekompaniet AS | Wholesale & retail | 2017 |
| Proventia AS | Professional & scientific | 2013 |
| Proøk AS | Professional & scientific | 1990 |
| Prunex AS | Professional & scientific | 2015 |
| Pt-Seals AS | Manufacturing | 2025 |
| Purenviro AS | Professional & scientific | 2010 |
| Purple Cow AS | Professional & scientific | 2023 |
| Purple Cow Entertainment AS | Professional & scientific | 2024 |
| Påsan AS | Health & social care | 2013 |
| Qingtor AS | Professional & scientific | 2005 |
| Quality International Investment AS | Professional & scientific | 2015 |
| R&D Tomteco AS | Information & communication | 2023 |
| R&F Eiendom AS | Real estate | 2024 |
| R.S. Eiendom AS | Real estate | 2020 |
| R1 Holding AS | | 2022 |
| R8 Property AS | Real estate | 2023 |
| Ra Holding AS | Financial services | 2005 |
| Rab Industri AS | Manufacturing | 2025 |
| Racetech AS | Wholesale & retail | 2025 |
| Raddel AS | Professional & scientific | 2023 |
| Radio Grenland AS | Information & communication | 1994 |
| Rafa Holding AS | Professional & scientific | 2016 |
| Rambo Consulting AS | Professional & scientific | 2018 |
| Rameko AS | Professional & scientific | 2005 |
| Ramter AS | Real estate | 2017 |
| Ranold AS | Professional & scientific | 2003 |
| Raveien Utbygging AS | Real estate | 2019 |
| Raw Invest AS | Real estate | 2015 |
| RDH AS | Real estate | 2014 |
| RDH Holding AS | Real estate | 2005 |
| Reagera AS | Professional & scientific | 2023 |
| Real Byggteknikk AS | Professional & scientific | 2022 |
| Redco AS | | 2023 |
| Redco Eiendom AS | Real estate | 2024 |
| Rederene Heimdal Og Finne AS | | 2023 |
| REDNING24 AS | Other services | 2003 |
| Redo Biosolutions AS | Energy | 2002 |
| Reflex Odd Lundeberg & Co | Wholesale & retail | 1960 |
| Reform AS | Real estate | 2025 |
| Regnskapsservice AS | Professional & scientific | 1969 |
| Reinha Invest AS | Financial services | 2005 |
| Reinha MK Invest AS | | 2023 |
| Reinha VK Invest AS | | 2023 |
| Reiss Holding AS | Real estate | 2018 |
| Remotek AS | Wholesale & retail | 2022 |
| Ren Frisør AS | Other services | 2012 |
| Reodor Invest AS | Professional & scientific | 2020 |
| Retroruss AS | Wholesale & retail | 2025 |
| Rett in Vest AS | | 2003 |
| RF Telemark Holding AS | | 2025 |
| RGL Holding AS | Real estate | 2005 |
| Ri Bryggeveien 2 AS | Real estate | 2015 |
| Rico AS | Real estate | 2003 |
| Riise Elektro Ans | Other services | 1995 |
| Riktig Eiendom AS | Real estate | 2015 |
| Rio Pizza Porsgrunn AS | Hospitality | 1997 |
| Ripegutu Nygård Holding AS | Wholesale & retail | 2015 |
| Risør Utvikling AS | Real estate | 2021 |