| Ontaxi AS | Oslo | 2025 |
| Ooc Cougar GmbH & Co KG | 22301 Hamburg | 2009 |
| OOCL SCAN BALTIC Norsk avdeling av utenlandsk foretak NUF | 8000 Århus C | 1996 |
| Op Mikalsen Transport AS | Rolvsøy | 2007 |
| Op Transport AS | Vinterbro | 2013 |
| Opedal Sjåfør Og Vikartjeneste AS | Lofthus | 2021 |
| Opedal Transport AS | Lofthus | 2013 |
| Ophuus AS | Røros | 2020 |
| Opp Fryseri AS | Oppdal | 2021 |
| Opp Og Ned Transport AS | Holter | 2002 |
| Oppdal Auto AS | Oppdal | 2013 |
| Oppdal Bilberging AS | Oppdal | 2001 |
| Oppdal Taxi SA | Oppdal | 1965 |
| Oppdal Thermotransport Ans | Oppdal | 2001 |
| Oppdal Transport AS | Grøa | 1992 |
| Opperud Transport Da | Tyristrand | 2010 |
| Oppkjøpsentralen AS | Porsgrunn | 1998 |
| Oppland Metall Transport AS | Hunndalen | 1998 |
| Oppleider AS | Salhus | 2021 |
| Opplev Haldenkanalen AS | Halden | 2022 |
| Oppsal Taxi AS | Oslo | 2023 |
| Opseth Og Kjelsnes AS | Førde | 2023 |
| Optimal Synergies AS | Vollen | 2018 |
| Optimal Transport, Sviland Da | Ålgård | 2016 |
| Optismart AS | Risør | 2025 |
| Ordy Delivery AS | Vestskogen | 2016 |
| Orheim Turbuss AS | Stårheim | 2007 |
| Orion Bulk KS | Nesttun | 2019 |
| Orion Transport Og Montasje AS | Knapstad | 2007 |
| Orkanger Containerterminal AS | Orkanger | 2020 |
| Orkdal Transport Holding AS | Orkanger | 2013 |
| Orkla Shipping & Trading AS | Orkanger | 1981 |
| Orkland Taxi AS | Orkanger | 1980 |
| Oro Tankers AS | Paradis | 2021 |
| Oromar AS | Holmestrand | 2007 |
| Orooj Mahmood AS | Fjerdingby | 2016 |
| Orrem Taxi AS | Molde | 2025 |
| Orrestad Holding AS | Sogndal | 2021 |
| Ortima Nuf | Lt-08221 Vilnius | 2024 |
| Ortra AS | Nordfjordeid | 1991 |
| Os Kranservice AS | Lepsøy | 2010 |
| Os Maskin AS | Lepsøy | 2001 |
| Os Maskin Transport AS | Lepsøy | 2012 |
| Os Norge AS | Oslo | 2026 |
| Os Parkering AS | Os | 2010 |
| Os Taxi AS | Os | 2004 |
| Os Transport AS | Sandnes | 2023 |
| Os Transport AS | Lørenskog | 1997 |
| Oscar Bud Og Transport Ans | Oslo | 2005 |
| Osen Taxi AS | Steinsdalen | 2020 |
| Osen Transport AS | Sira | 1989 |
| Osestølen Bilstall AS | Ustaoset | 2009 |
| Osi AS | Vestfossen | 2006 |
| Oskar Investment AS | Oslo | 2006 |
| Oskar' S Bud AS | Hell | 2016 |
| Oskar's Logistikk AS | Brårud | 2024 |
| Oslo Airport Cold Storage AS | Gardermoen | 2023 |
| Oslo App Taxi AS | Oslo | 2024 |
| Oslo Betongtransport AS | Årnes | 2012 |
| Oslo Bilhjelp AS | Oslo | 1995 |
| Oslo Blomsterservice AS | Oslo | 2026 |
| Oslo Bud & Blomsterservice AS | Oslo | 2012 |
| Oslo Bud & Vare AS | Skedsmokorset | 2014 |
| Oslo Budbil Formidling Ans | Oslo | 1991 |
| Oslo Budservice AS | Oslo | 1991 |
| Oslo Bulk Alpha AS | Oslo | 2019 |
| Oslo Bulk AS | Oslo | 2018 |
| Oslo Bulk Beta AS | Oslo | 2019 |
| Oslo Bulk Delta AS | Oslo | 2026 |
| Oslo Bulk Epsilon AS | Oslo | 2025 |
| Oslo Bulk Gamma AS | Oslo | 2024 |
| Oslo Bulk Kappa AS | Oslo | 2026 |
| Oslo Byrået AS | Oslo | 2021 |
| Oslo Båtmannsforretning A/S | Oslo | 1988 |
| Oslo Cab AS | Oslo | 2021 |
| Oslo Cabs AS | Gardermoen | 2017 |
| Oslo Capes AS | Oslo | 2026 |
| Oslo Caribbean Carrier AS | Oslo | 2018 |
| Oslo Chauffeur Service AS | Oslo | 2010 |
| Oslo Containerservice AS | Oslo | 1999 |
| Oslo Ekspert AS | Fetsund | 2021 |
| Oslo Express AS | Oslo | 2024 |
| Oslo Fjordcruise AS | Oslo | 1991 |
| Oslo Fjordways AS | Oslo | 2015 |
| Oslo Flex Logistikk Og Konstruksjon AS | Siggerud | 2020 |
| Oslo Flytte- Og Renholdservice AS | Lørenskog | 2024 |
| Oslo Flyttehjelp AS | Oslo | 2019 |
| Oslo Fraktservice AS | Drammen | 2024 |
| Oslo Fryselager AS | Oslo | 2014 |
| Oslo Green Taxi AS | Oslo | 2021 |
| Oslo Hjelpeservice AS | Oslo | 2026 |
| Oslo Kranbilservice AS | Gardermoen | 2023 |
| Oslo Line AS | Oslo | 1994 |
| Oslo Logistikk AS | Oslo | 2024 |
| Oslo Lufthavns Tankanlegg AS | Gardermoen | 1996 |
| Oslo Merchant Partners LNG AS | Oslo | 2021 |
| Oslo Minibuss AS | Oslo | 2020 |
| Oslo Og Akershus Transport AS | Hakadal | 2014 |
| Oslo Og Akershus Turbusser AS | Tranby | 1996 |
| Oslo Og Bærum Transport AS | Bekkestua | 2022 |