| Olderfjord Lodge AS | Russenes | 2022 |
| Oldervik Eiendom AS | Klæbu | 2024 |
| Oldervik Investment AS | Klæbu | 2019 |
| Ole & Vidars Hageservice Da | Sem | 1993 |
| Ole Erik Haugstad Limited Nuf | Enebakk | 2011 |
| Ole Johnny Amundsen AS | Åndalsnes | 2016 |
| Ole Mekk AS | Furnes | 2016 |
| Ole Morten Orset | Ørsta | 1999 |
| Ole Nygård AS | Ansnes | 2012 |
| Ole Wilhelmsen AS | Alta | 2023 |
| Ole-Ludvig Akre AS | Lommedalen | 1995 |
| Olebakkjen Holding AS | Fitjar | 2022 |
| Olenas Renholdstjenester AS | Haltdalen | 2025 |
| Olga AS | Oslo | 2011 |
| Oli Invest AS | Oslo | 2017 |
| Oliv Invest AS | Paradis | 2020 |
| Oliva Park AS | Grålum | 2018 |
| Oliven Reiser AS | Skien | 2021 |
| Oliver Travel AS | Røros | 2009 |
| OLS1 Holding AS | Marnardal | 2018 |
| Olsen AS | Oslo | 2014 |
| Olsen Aviation AS | Sandvika | 2011 |
| Olsen Cruise Service AS | Fyllingsdalen | 2016 |
| Olsen Eiendom Leknes AS | Leknes | 1990 |
| Olsen Management AS | Bekkjarvik | 1985 |
| Olsen Maskinentreprenør AS | Nordstrøno | 2015 |
| Olsen Og Gautestad Ans | Evje | 1999 |
| Olsen Og Stoveland AS | Søgne | 2024 |
| Olsen Utleie Nesodden AS | Nesoddtangen | 2023 |
| Olsen Vedlikeholdservice AS | Bergen | 2005 |
| Olseng Invest AS | Sarpsborg | 2015 |
| Olsens Service AS | Sandnes | 2020 |
| Olsrud Holding AS | Mosjøen | 2005 |
| Olssons Event AB | Se-652 09 Karlstad | 2018 |
| Olsvik Gard AS | Ørsta | 2019 |
| Olto Fleet AS | Evje | 2025 |
| Olufsen Værsego AS | Lurøy | 2022 |
| Olympic Boreas AS | Fosnavåg | 2022 |
| Olympic Crewing Mexico AS | Fosnavåg | 2015 |
| Olympic Nobo AS | Fosnavåg | 2025 |
| Olympic Notos AS | Fosnavåg | 2023 |
| Olympic Ocean AS | Fosnavåg | 2021 |
| Olympic Offshore Wind II AS | Fosnavåg | 2022 |
| Olympic Shipping AS | Fosnavåg | 1996 |
| Olympic Wind Holding AS | Fosnavåg | 2022 |
| Olympus Bidco | Se-145 63 Stockholm | 2023 |
| Om Hansen Holding AS | Melhus | 2020 |
| Om Kran AS | Alta | 2017 |
| Om Measuring Tools AS | Tromsø | 2009 |
| Om Rengjøring AS | Åros | 2026 |
| Om Utleie AS | Valestrandsfossen | 2013 |
| Omar's City Renhold AS | Trondheim | 2007 |
| Omars AS | Oslo | 2026 |
| Omb Investment AS | Bergen | 2019 |
| Omberg Hageservice AS | Auli | 1994 |
| Omega 365 Admin AS | Ølensvåg | 2016 |
| Omega Completion Technology Ltd | Aberdeen Ab21 Ogq | 2010 |
| Omega Innovation AS | His | 2003 |
| Omega Renhold AS | Laksevåg | 2024 |
| Omega Resource Group PLC Nuf | Stonehouse Gloucestershire Gl10 3Rf | 2009 |
| Omega Security AS | Kolbotn | 2025 |
| Omega Subsea Robotics AS | Ølensvåg | 2022 |
| Omg Utleige AS | Etne | 2019 |
| Omi Trans AS | Narvik | 2020 |
| Omica AS | Drammen | 2026 |
| Omis Travel Representation AB | Se-114 32 Stockholm | 2016 |
| Omnetric GmbH (Austria) | At-1210 Vienna | 2017 |
| Omniacare AS | Oslo | 2024 |
| Oms Poland | Pl-80-873 Gdansk | 2024 |
| Omservice AS | Laksevåg | 2014 |
| Omsorg for Hus Og Heim AS | Andenes | 2019 |
| Omsorg Pluss AS | Lødingen | 2024 |
| Omsorgshjerte Vikartjenester AS | Torød | 2024 |
| Omsorgsplan AS | Tønsberg | 2023 |
| Omtanken Bemmanning AS | Oslo | 2024 |
| Omv (Tunesien) Production GmbH | At-1020 Wien | 2020 |
| Omv Exploration & Production GmbH | At-1210 Vienna | 2006 |
| Omv International (CH) GmbH Nuf | Ch-6340 Baar | 2014 |
| Omv New Zealand Ltd | Nz-6001 Wellington | 2013 |
| Omv Petrom | Stavanger | 2013 |
| Omv Petrom Global Solutions SRL | Stavanger | 2016 |
| On Air AS | Lillehammer | 2000 |
| On Off Bemanning AS | Bergen | 2000 |
| On the Rocks Invest AS | Jar | 2007 |
| On-Ramp AS | Hagan | 2019 |
| On-Time AS | Drøbak | 2005 |
| ON2A4 | Dk-8700 Horsens | 2012 |
| Onb AS | Gjøvik | 2018 |
| Onboard Holding AS | Trondheim | 2021 |
| Onboard Norway AS | Trondheim | 2021 |
| Oncruiter AS | Son | 2020 |
| One More AS | Jar | 2026 |
| One Nice Arena Live AS | Oslo | 2019 |
| Oneint Lebal (Norway) Limited | London Ec1V 2Nx England | 2024 |
| Onergo AS | Stavanger | 2023 |
| Onestep AS | Oslo | 2014 |
| Onesubsea Cyprus Ltd | 7100 Larnaca | 2016 |
| Onetec AS | Tomrefjord | 2013 |
| Onkel Dags Kafferens AS | Hjellestad | 2013 |
| Only Group AS | Tromsø | 2022 |