| Otb AS | Real estate | 2013 |
| Outletsenteret AS | Wholesale & retail | 2025 |
| Oxum Eiendom AS | Real estate | 2016 |
| Oygarden AS | Real estate | 1994 |
| P Apartments AS | Real estate | 2025 |
| P O Berg AS | Hospitality | 1992 |
| P O Holding AS | Real estate | 2005 |
| P4 Parkering AS | Real estate | 2023 |
| Padel Universe Porsgrunn AS | Arts & recreation | 2021 |
| Padel Universe Skien AS | Arts & recreation | 2022 |
| Pagenode AS | Information & communication | 2020 |
| Palmelina AS | | 2026 |
| Pamam Holding AS | Financial services | 2016 |
| Pancom AS | Wholesale & retail | 2014 |
| Pancom Development AS | Real estate | 2021 |
| Pancom Management AS | Construction | 2016 |
| Pancom Oygarden Bolig AS | Real estate | 2018 |
| Pancom Property AS | Real estate | 2014 |
| Pancom Utvikling AS | Real estate | 2014 |
| Panorama Auto AS | Wholesale & retail | 2016 |
| Pans Veg Tomt AS | Real estate | 2019 |
| Pans Veg Utbygging AS | Real estate | 2019 |
| Papillon Holding AS | Real estate | 2014 |
| Park Eiendom AS | Real estate | 1992 |
| Park Frisør Da | Other services | 2000 |
| Park Frisører AS | Other services | 2008 |
| Park Nattklubb AS | Hospitality | 2025 |
| Park Pizza Grill Da | Hospitality | 2024 |
| Park Saunter AS | Wholesale & retail | 2025 |
| Pasa AS | Real estate | 1997 |
| Pasquinell AS | Wholesale & retail | 1988 |
| Paulsen Telecom AS | Construction | 2020 |
| Pavels Innovation AS | | 2004 |
| Paxpo AS | Professional & scientific | 2018 |
| Pbbl Bolig AS | Real estate | 2018 |
| Pbbl Jernbanegaten Næringseiendom AS | Real estate | 2004 |
| Pbbl Utbygging AS | Real estate | 2005 |
| PCP AS | Wholesale & retail | 2017 |
| Peculium AS | Real estate | 2006 |
| Peculium Bolig AS | Real estate | 2025 |
| Peculium Invest AS | Real estate | 2017 |
| Pep-Talk AS | | 2005 |
| Pepperl+Fuchs AS | Wholesale & retail | 1968 |
| Per Johan Schanke Invest AS | Real estate | 2019 |
| Per Øverlands Eiendomsselskap AS | Construction | 1989 |
| Per-Aage.Com AS | Professional & scientific | 2013 |
| Perinco AS | Real estate | 2013 |
| Pers Byggservice AS | Real estate | 2012 |
| PF Hera | Construction | 1998 |
| PG - Byggutvikling AS | Construction | 2012 |
| PG Bygg Og Eiendom AS | Construction | 2021 |
| PG Utvikling AS | Real estate | 2017 |
| Pg-Service AS | Other services | 2007 |
| Pga AS | Professional & scientific | 2015 |
| Phenix AS | Financial services | 2019 |
| Piben AS | Real estate | 2010 |
| Pigeon Vitality AS | Information & communication | 2000 |
| Pikene Ved Broen Da | Wholesale & retail | 2001 |
| Pimpyourkid Da | Wholesale & retail | 2013 |
| Pippen Eiendom AS | Real estate | 2025 |
| Pire AS | Real estate | 2021 |
| Piteå Holding AS | Professional & scientific | 2007 |
| Pizza Kompaniet AS | Hospitality | 2017 |
| Pizzeria Seval AS | Hospitality | 2005 |
| Plan B IT AS | Information & communication | 2019 |
| Plan- Og Bygg Konsulent AS | Professional & scientific | 2014 |
| Plastech Da | Professional & scientific | 2025 |
| Plutos AS | Arts & recreation | 2013 |
| PM Knutsen Holding AS | Professional & scientific | 2020 |
| PM Telemark AS | Real estate | 2009 |
| Pmathisen AS | | 2021 |
| PN Porsgrunn AS | Hospitality | 2021 |
| Poesiforlaget AS | Information & communication | 2026 |
| Polar Grenland AS | Manufacturing | 2007 |
| Polaris Nord AS | | 2026 |
| Pool Works AS | Wholesale & retail | 2022 |
| Pors Dekkmann Bil Og Båtpleie AS | Other services | 2021 |
| Pors Entreprenør AS | Construction | 2020 |
| Pors Gjerdefabrikk AS | Manufacturing | 2002 |
| Porselensfabrikken Energi AS | Real estate | 2011 |
| Porselensfabrikken Næringspark AS | Real estate | 2009 |
| Porselensklinikken AS | Wholesale & retail | 1991 |
| Porselensvegen 32 AS | Real estate | 2021 |
| Porsgrunds Porselænsfabrik AS | Manufacturing | 1885 |
| Porsgrunn Armering AS | Construction | 1986 |
| Porsgrunn Asia Mat AS | Wholesale & retail | 2020 |
| Porsgrunn Auto AS | Wholesale & retail | 2024 |
| Porsgrunn Blomsterforretning AS | Wholesale & retail | 2024 |
| Porsgrunn Bolig AS | Real estate | 2010 |
| Porsgrunn Brønnboring AS | Construction | 2012 |
| Porsgrunn Elsykkel AS | Wholesale & retail | 2026 |
| Porsgrunn Engineering AS | Professional & scientific | 2024 |
| Porsgrunn Folkets Hus AS | Real estate | 1998 |
| Porsgrunn Helsepark AS | Real estate | 2021 |
| Porsgrunn Kiropraktorklinikk AS | Health & social care | 2006 |
| Porsgrunn Kjerneboring AS | Construction | 2024 |
| Porsgrunn Kontorbygg Holding AS | Real estate | 2009 |
| Porsgrunn Ladetjeneste Svendsen & Kassa Ans | Manufacturing | 1987 |
| Porsgrunn Legesenter AS | Health & social care | 2013 |
| Porsgrunn Lungeklinikk AS | Health & social care | 2018 |