| Only Invest AS | Tromsø | 2020 |
| Onnec Denmark Aps Nuf | 5220 Odense Sø | 2025 |
| Onnec Ireland Limited Nuf | Ie-Dublin 18 | 2024 |
| Onpro AS | Tolvsrød | 2020 |
| Ons Invest II AS | Oslo | 2005 |
| Ons Ship Finance AS | Oslo | 2005 |
| Ons Ship Invest 1 AS | Oslo | 2017 |
| Onsite Power Exchange Europe GmbH | De-44139 Dortmund | 2024 |
| Onsite Security AS | Hamar | 2019 |
| Onsite Technologies AS | Hamar | 2025 |
| Onstage AS | Krokstadelva | 2022 |
| Onsøy Lyd & Lys AS | Engelsviken | 2018 |
| Onsøy Mur & Anlegg Eiendom Ans | Gressvik | 1994 |
| Onsøy Snø Og Utemiljø AS | Gressvik | 2014 |
| Onyx Centersource Spain, S.A | Es-41013 Seville | 2020 |
| Ooo Flait | 183039 Murmasnk | 2007 |
| Ooo Flait Group | Ru-183039 Murmansk | 2011 |
| Op Service AS | Storforsheia | 2026 |
| Opab AS | Sandnessjøen | 2025 |
| Opas Kreditt AS | Gressvik | 1995 |
| Opb Services AS | Lierskogen | 1997 |
| Opc Asset Holdings AS | Drøbak | 2024 |
| Opdal Gård Holding AS | Øye | 2005 |
| Opedal Utleige AS | Lofthus | 2007 |
| Opedia Holding AS | Lillestrøm | 2008 |
| Open Klasse AS | Voss | 2015 |
| Open Payments Europe AS | Fjerdingby | 2024 |
| Open Road Tours & Travel AS | Evenskjer | 2016 |
| Open Tab AS | Oslo | 2026 |
| Opera 60 AS | Trondheim | 2017 |
| Operadora Portuaria De Lazaro Cardenas Sa.De C.V. | Bergen | 2004 |
| Operalåven AS | Ål | 2021 |
| Operation Arctic Events AS | Rognan | 2018 |
| Operatribunen AS | Nesodden | 2008 |
| Opgangssagen AS | Jar | 1998 |
| Opheim Guest Service AS | Olden | 2025 |
| Opheim Invest AS | Bønes | 2005 |
| Opl Consulting AS | Oslo | 2005 |
| Opn Nuf | Kristiansand S | 2008 |
| Opn Organisasjon Prosjekt Og Næringsutvikling AS | Oslo | 1996 |
| Oppdag Bygda AS | Dalholen | 2024 |
| Oppdal Bygdeservice SA | Oppdal | 2015 |
| Oppdal Eiendomsforvaltning AS | Molde | 2025 |
| Oppdal Live AS | Trondheim | 2017 |
| Oppgjør Nord AS | Alta | 2021 |
| Oppgrader AS | Jevnaker | 2011 |
| Oppland Arrangement Da | Etnedal | 1991 |
| Oppland Byggvask AS | Gjøvik | 2014 |
| Opplei AS | Strømmen | 2026 |
| Opplett Bergen AS | Bergen | 2024 |
| Opplev Afrika AS | Stavanger | 2020 |
| Opplev Event AS | Sarpsborg | 2022 |
| Opplev Finnmark AS | Talvik | 2018 |
| Opplev Gålå SA | Gålå | 2018 |
| Opplev Hidra AS | Hidrasund | 2021 |
| Opplev Markabygda SA | Markabygda | 2022 |
| Opplev Nord AS | Bodø | 2019 |
| Opplev Rendalen SA | Rendalen | 2020 |
| Opplev Ryfylke AS | Jørpeland | 2024 |
| Opplev Røros AS | Røros | 2008 |
| Opplev Solbakke AS | Vesterøy | 2022 |
| Opplev Undredal AS | Undredal | 2006 |
| Opplevelse AS | Bergen | 2016 |
| Opplysningen 1881 AS | Lysaker | 2010 |
| Opplysningskontoret for Vin Ans | Kvinesdal | 2000 |
| Opplyst Elektro AS | Kolbotn | 2017 |
| Oppsal Multiservice AS | Lillestrøm | 2019 |
| Opptur Villmarksopplevelser AS | Svarstad | 1998 |
| Oppussing Og Rengjøring AS | Lommedalen | 2012 |
| Opr Crew Limited | Guernsey Gy1 2Ja | 2024 |
| Ops AS | Namsos | 2025 |
| Optasense Norway Nuf | Asker | 2020 |
| Optice AS | Kongsvinger | 2012 |
| Optima Eiendom AS | Sandnes | 2024 |
| Optima Solutions OY | Fi-01510 Vantaa | 2018 |
| Optimal Drift & Service AS | Gimse | 2023 |
| Optimal Drift AS | Tolvsrød | 2024 |
| Optimal Finans AS | Narvik | 2017 |
| Optimal Performance Services AS | Fetsund | 2025 |
| Optimal Rekruttering AS | Oslo | 2019 |
| Optimal Sikkerhetssystemer AS | Sarpsborg | 2012 |
| Optimal Utleie AS | Gamle Fredrikstad | 2017 |
| Optimal Ventilasjon AS | Magnor | 2025 |
| Optimaljakt AS | Maura | 2023 |
| Optimalt Renhold AS | Oslo | 2015 |
| Optimisten Rengjøringsbyrå Da | Drammen | 1996 |
| Optimus Projects Limited | Aberdeen Ab15 4Al | 2015 |
| Optinomos AB | 98199 Kiruna | 2008 |
| Optos PLC | Fife Ky11 8Gr Scotland | 2007 |
| Optoteam AS | Oslo | 2021 |
| Optoteam Holding AS | Oslo | 2018 |
| Opus Finance Recruitment AS | Oslo | 2011 |
| Opus International AS | Melsomvik | 1997 |
| Opus Recruitment Solutions Limited | Bristol Bs1 3Ag | 2014 |
| Opus Team AS | Stranda | 2009 |
| Opus Team Midsund AS | Stranda | 2012 |
| Opuscapita Competence Center Sia | Riga Lv-1004 | 2014 |
| Oracle Deutschland GmbH | De-80992 Munchen | 2001 |
| Oracle Egypt Ltd | Eg-Cairo | 2013 |
| Oracle Finland OY | Fi-02200 Espoo | 2008 |