| Olav Aakre Holding AS | | 2022 |
| Oldroyd Engros AS | Wholesale & retail | 2021 |
| Ole Lerbrekk Holding AS | Arts & recreation | 2005 |
| Oliven Reiser AS | Administrative & support | 2021 |
| Oljeindustriens Kompetansecenter AS | Professional & scientific | 1989 |
| Oljetorget AS | Wholesale & retail | 2013 |
| Ollestad Holding AS | Real estate | 2007 |
| Olsson Snekkerservice AS | Construction | 2026 |
| Oluf Rasmussen AS | Information & communication | 1981 |
| Omgi AS | Construction | 2015 |
| Omk Invest AS | | 2021 |
| Ommuruca AS | Health & social care | 2017 |
| Omni Vision AB | Wholesale & retail | 2006 |
| One Accounting AS | Professional & scientific | 2018 |
| One Invest AS | | 2022 |
| One Ring Holdings AS | | 2026 |
| Onera Fritidseiendom AS | Real estate | 2005 |
| Onera Næring AS | Real estate | 2022 |
| ONLY1LIFE AS | Other services | 2017 |
| Ootc Productions AS | Arts & recreation | 2021 |
| Opa Helse AS | Health & social care | 2015 |
| Opplæringskontoret for Bilfag I Telemark AS | Education | 1995 |
| Opsahl Ur & Optikk AS | Wholesale & retail | 1979 |
| Optimal Brannsikkerhet AS | Professional & scientific | 2022 |
| Optimal Bygg & Betong AS | Construction | 2023 |
| Optimalhelse Senter Skien AS | Health & social care | 2013 |
| Optimus Byggutvikling AS | Real estate | 2015 |
| Oralkirurg Anne Aasen AS | Health & social care | 2021 |
| Origami Paperworks AS | Professional & scientific | 2019 |
| Origo Finans AS | Real estate | 2007 |
| Ork AS | Construction | 2006 |
| Orsted Norway Services AS | Professional & scientific | 2023 |
| OSB1 AS | Real estate | 2024 |
| Oscars Invest AS | Construction | 2013 |
| Oscarsgate 2B AS | Wholesale & retail | 2017 |
| Osiris Treningssenter Skien AS | Real estate | 2015 |
| Ospeskog AS | Professional & scientific | 2020 |
| Otern AS | Transport & logistics | 2023 |
| Otterstad Holding AS | | 2022 |
| Oyb 245 Holding AS | | 2023 |
| P Håkonsen Eiendom AS | Real estate | 2000 |
| P. Å. Husby Holding AS | Financial services | 2005 |
| P.Borgersen Invest AS | | 2016 |
| Paabygg AS | Construction | 2014 |
| Pagan's Mind Da | Information & communication | 2009 |
| Pahlen International AS | Wholesale & retail | 1975 |
| Paho AS | Real estate | 2006 |
| Pakkepost AS | Transport & logistics | 2020 |
| Paks Consulting Da | Information & communication | 2007 |
| Panacea Holding AS | Health & social care | 2018 |
| Panacea Klinikk AS | Health & social care | 2021 |
| Pandora Eiendom AS | Real estate | 2019 |
| Panem Et Circenses Limited Nuf | | 2025 |
| Panorama Hjemmetjenester AS | Administrative & support | 2020 |
| Paragon Drift AS | Wholesale & retail | 2018 |
| Paragon Eiendom AS | Real estate | 2018 |
| Paragon Holding AS | Real estate | 2013 |
| Paragon Invest AS | Real estate | 2018 |
| Park Event AS | Administrative & support | 2013 |
| Park Pizza Grillen AS | Hospitality | 2025 |
| Parkeringsplasser AS | Construction | 2016 |
| Parkjazz AS | Arts & recreation | 2019 |
| Parkveien 51 a AS | Real estate | 1999 |
| Parmesana Restaurant AS | Hospitality | 2022 |
| Partsrederiet August Petursson Ans | Agriculture & fishing | 2007 |
| Partygrossisten AS | Wholesale & retail | 2015 |
| Partytelt Utleie AS | Administrative & support | 2014 |
| Pasios Haksol AS | | 2026 |
| Pasios Invest AS | Real estate | 2017 |
| Pasios Lex AS | | 2026 |
| Pasios Paragon AS | | 2026 |
| Passione Della Bicicletta AS | Real estate | 2015 |
| Paulsen Consult AS | Professional & scientific | 2000 |
| Pavo Holding AS | Real estate | 2011 |
| Payee AS | | 2021 |
| Pazzo Restaurantdrift AS | Hospitality | 2025 |
| PBJ Holding AS | Financial services | 2012 |
| PCC Norway AS | Manufacturing | 2014 |
| Pe Holding AS | Financial services | 2005 |
| Peder Goberg Holding AS | Real estate | 2015 |
| Peisovnspesialisten AS | Wholesale & retail | 2004 |
| Pelianto AS | Wholesale & retail | 2025 |
| Pelifax AS | Professional & scientific | 2023 |
| Pelotongveien 2 AS | Real estate | 1996 |
| Pelsklar AS | Other services | 2025 |
| Pense Invest AS | Financial services | 2005 |
| Pepita Skien AS | Wholesale & retail | 2004 |
| Per Haakonsen Holding AS | | 2022 |
| Perry Bar AS | Hospitality | 2009 |
| Personaltjenester Telemark AS | Administrative & support | 2001 |
| Pertrine AS | Health & social care | 2025 |
| Petersborg Melk Da | Agriculture & fishing | 2003 |
| Petit Grafisk AS | Manufacturing | 1997 |
| PF Clothing AS | Wholesale & retail | 2024 |
| PF Invest AS | Water & waste | 2005 |
| PH Norway AS | Professional & scientific | 2020 |
| Phi AS | Real estate | 2020 |
| Pic'N'Boid Holding AS | | 2018 |
| Pinzano Norge AS | Wholesale & retail | 1996 |
| Piperehabilitering AS | Construction | 2025 |