| Organic AS | Tolvsrød | 2018 |
| Organisasjonspsykolog Jon E. Jacobsen AS | Kråkerøy | 2011 |
| Organisasjonspsykologen AS | Stavanger | 2017 |
| Organisasjonspsykologene Skare AS | Tromsø | 2016 |
| Organisk Rådgivning AS | Trondheim | 2016 |
| Organos Norway | Fornebu | 2021 |
| Orgevo AS | Tolvsrød | 2012 |
| Orglos AS | Våler I Østfold | 2025 |
| Orgproff AS | Oslo | 2018 |
| Orgservice AS | Oslo | 2017 |
| Orgservice Regnskap AS | Oslo | 2024 |
| Orh Holding AS | Stryn | 2020 |
| Orh Investering AS | Sandnes | 2020 |
| Oriaku Studio AS | Oslo | 2025 |
| Oriana AS | Torangsvåg | 2024 |
| Oriber AS | Bergen | 2017 |
| Orient Hsse AS | Sandnes | 2017 |
| Orient Marine AS | Bodø | 2020 |
| Oriented Accounting AS | Lillestrøm | 2025 |
| Orientekspressen AS | Vikhammer | 2005 |
| Origami Paperworks AS | Skien | 2019 |
| Origami Studios AS | Lørenskog | 2020 |
| Original Teknologi AS | Kongsberg | 2016 |
| Originaldekor AS | Kongsvinger | 2021 |
| Origination AS | Oslo | 2022 |
| Originatorz IT & Software Professionals AS | Lier | 2023 |
| Origo Alpha AS | Nesøya | 2014 |
| Origo Alpha Mellom AS | Nesøya | 2021 |
| Origo Arkitektgruppe AS | Bergen | 1987 |
| Origo Byggprosjekt AS | Gjøvik | 2006 |
| Origo Consulting AS | Sandnes | 2008 |
| Origo Financial Partners AS | Bekkestua | 2011 |
| Origo Group Sverige AB Nuf | Se-118 46 Stockholm | 2024 |
| Origo Solutions AS | Kristiansand S | 2000 |
| Origo Test & Inspection AS | Avaldsnes | 2014 |
| Origo Ventures AS | Oslo | 2023 |
| Origon AS | Lysaker | 2024 |
| Origon Holding AS | Lysaker | 2024 |
| Orin Advisory AS | Oslo | 2026 |
| Orinor AS | Alta | 2001 |
| Orion & Partners AS | Oslo | 2002 |
| Orion Engineering Service Ltd | Inverness Iv2 6Aa Scotland | 1999 |
| Orion Media AS | Stavanger | 2018 |
| Orion Media Holding AS | Stavanger | 2018 |
| Orion Offshore AS | Rådal | 2017 |
| Orion Prospects AS | Oslo | 2023 |
| Orion Revisjon AS | Sandefjord | 2016 |
| Orion Search International AS | Oslo | 2017 |
| Oriri Norge AS | Oslo | 2025 |
| Orivo AS | Molde | 2013 |
| Orizuru AS | Lillestrøm | 2019 |
| Orizzontes AS | Oslo | 2012 |
| Orka Norsk Energi AS | Haltdalen | 2019 |
| Orkan Konsult AS | Stavanger | 2013 |
| Orkas AS | Oslo | 2012 |
| Orkdal Regnskapskontor SA | Fannrem | 2001 |
| Orkestra AS | Skedsmokorset | 2018 |
| Orkla Care | Dk-2635 Ishøj | 2019 |
| Orkla Engineering AS | Orkanger | 2006 |
| Orkla Financial Services AS | Oslo | 2022 |
| Orkla Holding AS | Tiller | 2003 |
| Orkla Nova AS | Orkanger | 2025 |
| Orkla Regnskap AS | Tiller | 2012 |
| Orkla Revisjon AS | Tiller | 2020 |
| Orkla Sparebank Regnskap AS | Meldal | 2025 |
| Orkland Arkitektkontor AS | Orkanger | 2016 |
| Orkland Regnskap AS | Lensvik | 2024 |
| Orlen Energy Trading GmbH | De-80636 München | 2019 |
| Orm Holding AS | Lysaker | 2016 |
| Ormesteinen AS | Ulsteinvik | 2007 |
| Ormstad Regnskap AS | Sørum | 2017 |
| Ornatus Trading AS | Gurskøy | 2025 |
| Ornor AS | Oslo | 2022 |
| Oron Invest AS | Kristiansand S | 2006 |
| Oronsay Well Services Ltd | Dd1 14Rl Arbroath | 2009 |
| Oroquita AS | Tønsberg | 2014 |
| Orpas Oslo AS | Oslo | 2014 |
| Orphan Diagnostics AS | Oslo | 2016 |
| Orpheus Consulting Engineers Ltd | Hatherton Cannock Ws11 0E | 2011 |
| Orre AS | Åsgårdstrand | 2002 |
| Orry-San Holding AS | Oslo | 2021 |
| Ors Consulting AS | Oslo | 2013 |
| Ors Systemer AS | Sandnes | 2020 |
| Orsem AS | Tananger | 2016 |
| Orso Vero AS | Drøbak | 2007 |
| Orstad AS | Bryne | 2014 |
| Orstad Revisjon AS | Bryne | 2014 |
| Orstad Rådgivning AS | Bryne | 1998 |
| Orsted Norway Services AS | Skien | 2023 |
| Orsted Polska of Services SP. Z.O.O. | Pl-00801 Warsaw | 2024 |
| Orten Advise AS | Midsund | 2017 |
| Orthecta AS | Lørenskog | 2021 |
| Orthrus Project Management AS | Slattum | 2020 |
| Ortocon AS | Oslo | 2015 |
| Ortus Holding AS | Bergen | 2018 |
| Ortygia AS | Oslo | 2005 |
| Oruds Prosjektservice AS | Halden | 2006 |
| Orv Consulting AS | Krokstadelva | 2016 |
| Orv Holding AS | Stryn | 2009 |
| Orvekst Invest AS | Sande I Vestfold | 2005 |