| Offshore Preservation Services Limited | Ts23 3Ld Billingham Cleveland | 2021 |
| Offshore Project Services Limited | Ennis Co Clare | 2015 |
| Offshore Qualific AS | Stavanger | 2022 |
| Offshore Sensing AS | Sandsli | 2014 |
| Offshore Subsea Services Ltd Nuf | Iv2 6Fg Inverness | 2026 |
| Offshore Technical Compliance LLC Nuf | Us-70433-8848 Covington, Louisiana | 2025 |
| Offshore Technology AS | Alversund | 2011 |
| Offshore Technology Partner AS | Sola | 2010 |
| Offshore Wind Advisor AS | Bærums Verk | 2022 |
| Offshore Wind Design AS | Hamar | 2021 |
| Offshore-Energy AS | Stavanger | 2026 |
| Offshoreconsult AS | Nedenes | 2023 |
| Offshoreveien AS | Skien | 2020 |
| Offtech AS | Sola | 2012 |
| Oficío AS | Oslo | 2024 |
| Ofl AS | Os | 2024 |
| Oflat Media AS | Blystadlia | 2024 |
| Ofo Accounting AS | Oslo | 2026 |
| Ofo Holding AS | Oslo | 2024 |
| Ofo Services AS | Oslo | 2024 |
| Oform AS | Son | 2021 |
| Ofoten Consensus AS | Nordberg | 2015 |
| Ofoten Takst AS | Narvik | 1990 |
| Ofoten Takstforretning Holding AS | Narvik | 2020 |
| Ofotlab AS | Myklebostad | 2017 |
| Ofp Produkt AS | Arendal | 2022 |
| Oftedal Investering AS | Sola | 2022 |
| Oftedal Revisjon & Rådgivning AS | Stavanger | 2023 |
| Often Mineral AS | Bru | 2015 |
| Og Prosjekt AS | Hemsedal | 2007 |
| Ogai AS | Oslo | 2026 |
| Ogci/Petroskills Ltd | Ok 35448 | 2010 |
| Oge Solutions AS | Langhus | 2015 |
| Oggi Interiør Og Design AS | Nesøya | 2006 |
| Ogm AI Apps&Arts AS | Førresfjorden | 2026 |
| Ognøy Industri Service AS | Bokn | 2017 |
| Ogpro AS | Hafrsfjord | 2014 |
| Ogri AS | Sande I Vestfold | 2005 |
| Ogri Consulting AS | Sande I Vestfold | 2017 |
| Ogu AS | Hafrsfjord | 2024 |
| Oh Mama AS | Nesoddtangen | 2005 |
| Oh My Nuf | Oslo | 2017 |
| Oh Spell AS | Arendal | 2019 |
| Ohc Arkitektur & Design AS | Jar | 2001 |
| Ohh Entertainment AS | Sundebru | 2017 |
| Ohjem AS | Skjetten | 2026 |
| Ohjoy Ventures AS | Bergen | 2023 |
| Ohk Consult AS | Tromsø | 2005 |
| Ohlsoncontrols AS | Asker | 2019 |
| Ohm Bjellands Rederi AS | Haugesund | 2017 |
| Ohmega Holding AS | Stavanger | 2011 |
| Ohmw AS | Oslo | 2024 |
| Ohoy Systems AS | Stavanger | 2018 |
| Ohp AS | Harstad | 2013 |
| Ohs Holding AS | Drammen | 2005 |
| Oidid Ios Ltd | Monrose Dd10 8Ud Scotland | 2019 |
| Oik Completion AS | Stavanger | 2022 |
| Oiko AS | Risør | 1989 |
| Oikos Skjennum Holding AS | Åsgreina | 2020 |
| Oil & Gas Consultants Limited | Stornaway Hs1 2Dz Scotland | 2011 |
| Oil & Gas Service and AI Tools AS | Fåberg | 2026 |
| Oil Consultants Norway AS | Stavanger | 2020 |
| Oil Consulting AS | Trondheim | 2013 |
| Oil Extreme Europe AS | Paradis | 1986 |
| Oil Partners Int Limited | Hs1 2Ds Stornoway Isle Of Lewis | 2009 |
| Oil Ship Services - Norway AS | Lierstranda | 2013 |
| Oil Spill Response (Swis) Norway AS | Tananger | 2016 |
| Oil Spill Response Ltd | London W1H 7Al | 2011 |
| Oilcraft AS | Ålesund | 2013 |
| Oilers Event AS | Stavanger | 2017 |
| Oilfield Drilling Invest AS | Hafrsfjord | 2018 |
| Oilfield Production Consultants (Opc) Norge AS | Stavanger | 2013 |
| Oilfield Production Support Group Lmimited Nuf | Sandnes | 1995 |
| Oilrox AS | Langhus | 2014 |
| Oim Consultant AS | Jørpeland | 2021 |
| Oim Norway AS | Orkanger | 2026 |
| Oimacon AS | Rådal | 2014 |
| Oioi AS | Lørenskog | 2019 |
| Oioi Eiendom AS | Lørenskog | 2020 |
| Oioioi AS | Oslo | 2021 |
| Oisann Engineering AS | Søreidgrend | 2016 |
| Oj Consulting AS | Laksevåg | 2020 |
| Oj Productions AS | Høvik | 2014 |
| Oj! Konsept AS | Elverum | 2018 |
| Oja Holding AS | Auli | 2011 |
| Ojals AS | Oslo | 2005 |
| Ojan AS | Oslo | 2005 |
| Ojg Support AS | Kongsberg | 2017 |
| Ojk Rådgivning AS | Årnes | 2025 |
| Ojn Invest AS | Stavanger | 1998 |
| Ojrd AS | Trondheim | 2013 |
| Ojsann AS | Yven | 2018 |
| Ojt Holding AS | Oslo | 1992 |
| Ojvs Management AS | Molde | 2024 |
| Ok DAL1 AS | Uggdal | 2014 |
| Ok Lande Holding AS | Oslo | 2023 |
| Ok Partners AS | Trondheim | 2026 |
| Ok Regnskap AS | Lyngdal | 2024 |
| Ok Regnskap Invest AS | Oslo | 1987 |
| Ok Senior AS | Holmefjord | 1993 |