| Oslo & Akershus Graveservice AS | Kløfta | 2018 |
| Oslo & Akershus Svakstrøm AS | Fjerdingby | 2006 |
| Oslo & Follo Byggtjenester AS | Vinterbro | 2019 |
| Oslo & Follo Graveservice AS | Ås | 2015 |
| Oslo & Viken Graveservice Nuf | Oslo | 2021 |
| Oslo & Viken Rørlegger AS | Oslo | 2021 |
| Oslo / Akershus Bygg Og Montasje AS | Oslo | 2016 |
| Oslo Akershus Elektro Og Klima AS | Oslo | 2010 |
| Oslo Bad & Flis AS | Oslo | 2023 |
| Oslo Bad & Renovering AS | Oslo | 2014 |
| Oslo Bad & Snekkeri AS | Fjerdingby | 2026 |
| Oslo Bad AS | Oslo | 2010 |
| Oslo Baderom & Byggentreprenør AS | Oslo | 2021 |
| Oslo Betongsaging Og Boring A/S | Oslo | 1988 |
| Oslo Blikkenslagermester AS | Oslo | 2019 |
| Oslo Blåseisolering AS | Lillestrøm | 2025 |
| Oslo Boligteknikk AS | Oslo | 2023 |
| Oslo Bor & Riv AS | Oslo | 2021 |
| Oslo Brannsikring AS | Oslo | 2003 |
| Oslo Brannteknikk AS | Kjeller | 2025 |
| Oslo Bygg & VVS AS | Oslo | 2021 |
| Oslo Bygg AS | Oslo | 2022 |
| Oslo Bygg Maler AS | Lørenskog | 2015 |
| Oslo Bygg Miljø AS | Snarøya | 2022 |
| Oslo Bygg Og Eiendom AS | Oslo | 1996 |
| Oslo Bygg Og Håndverk AS | Oslo | 2026 |
| Oslo Bygg Og Restaurering AS | Stabekk | 2024 |
| Oslo Bygg Og Rør AS | Oslo | 2021 |
| Oslo Bygg Og Taksering AS | Oslo | 2021 |
| Oslo Bygg Og Vaktmestertjenester AS | Oslo | 2023 |
| Oslo Bygg T AS | Oslo | 2023 |
| Oslo Bygg Teknikk AS | Oslo | 2014 |
| Oslo Bygg, Drift Og Vedlikehold AS | Oslo | 2023 |
| Oslo Byggassistanse AS | Sofiemyr | 2015 |
| Oslo Byggconsult AS | Oslo | 2019 |
| Oslo Byggentreprenør AS | Oslo | 1988 |
| Oslo Byggfornyelse AS | Tjøme | 2007 |
| Oslo Byggfornying Da | Oslo | 2013 |
| Oslo Bygginnredning AS | Oslo | 2012 |
| Oslo Byggmester 1 AS | Nesøya | 2026 |
| Oslo Byggmester Service Drift AS | Skarnes | 2023 |
| Oslo Byggrehab AS | Oslo | 2016 |
| Oslo Byggrehabilitering AS | Oslo | 2016 |
| Oslo Byggsenter AS | Oslo | 2016 |
| Oslo Byggservice AS | Oslo | 2014 |
| Oslo Byggtek AS | Oslo | 2026 |
| Oslo Byggtjenester AS | Oslo | 2024 |
| Oslo Bærum Vann & Varme AS | Vøyenenga | 2020 |
| Oslo Communication AS | Auli | 2018 |
| Oslo Construction AS | Oslo | 2025 |
| Oslo Cruise Terminal AS | Oslo | 2018 |
| Oslo Drift Og Vedlikehold AS | Skedsmokorset | 2018 |
| Oslo El Installasjon AS | Oslo | 1994 |
| Oslo Electro Company AS | Oslo | 1992 |
| Oslo Elektriker Service AS | Oslo | 2004 |
| Oslo Elektriske AS | Oslo | 1991 |
| Oslo Elektro & Rør AS | Lørenskog | 2019 |
| Oslo Elektro Tech AS | Jar | 2016 |
| Oslo Elektroinstallasjon AS | Oslo | 2014 |
| Oslo Entreprenør AS | Oslo | 1992 |
| Oslo Entreprenør Smith AS | Oslo | 2024 |
| Oslo Epoxybelegg AS | Ytre Enebakk | 2018 |
| Oslo Fasade AS | Oslo | 2021 |
| Oslo Fasade Murmester AS | Oslo | 2021 |
| Oslo Fasaderehabilitering AS | Oslo | 2024 |
| Oslo Flis Og Bad AS | Oslo | 2020 |
| Oslo Glass & Vindu AS | Oslo | 1980 |
| Oslo Glass Og Rørleggerservice AS | Fetsund | 2026 |
| Oslo Graveteknikk AS | Gardermoen | 2023 |
| Oslo Graving Og Betong AS | Oslo | 2026 |
| Oslo Grunnarbeid AS | Oslo | 2021 |
| Oslo Håndverk Service AS | Oslo | 2016 |
| Oslo Håndverkslag AS | Oslo | 2026 |
| Oslo Håndverksmester AS | Oslo | 2025 |
| Oslo Innredning AS | Oslo | 2024 |
| Oslo Isolasjonsservice AS | Oslo | 1986 |
| Oslo Kjøleservice AS | Oslo | 2024 |
| Oslo Kjøleteknikk AS | Oslo | 2015 |
| Oslo Kvadrat AS | Oslo | 2026 |
| Oslo Landskap AS | Oslo | 2024 |
| Oslo Malerbedrift AS | Oslo | 2007 |
| Oslo Malerfirma AS | Oslo | 2020 |
| Oslo Malermester AS | Oslo | 2022 |
| Oslo Malermester Forretning AS | Oslo | 2015 |
| Oslo Malerservice Og Bygg AS | Oslo | 2004 |
| Oslo Malerteknikk AS | Lysaker | 2022 |
| Oslo Maskinservice AS | Bødalen | 2008 |
| Oslo Membranservice AS | Oslo | 1997 |
| Oslo Mesterbygg AS | Elverum | 2024 |
| Oslo Mikrosement AS | Hagan | 2024 |
| Oslo Mikrosement Og Mur AS | Oslo | 2024 |
| Oslo Multi Service AS | Tomter | 2025 |
| Oslo Mur & Bygg AS | Oslo | 2020 |
| Oslo Mur Og Flis AS | Oslo | 2026 |
| Oslo Murbygg AS | Oslo | 2023 |
| Oslo Murerne AS | Ytre Enebakk | 2002 |
| Oslo Murmesterbedrift AS | Oslo | 2012 |
| Oslo Og Akershus Drenering Og Byggservice AS | Vestby | 2026 |
| Oslo Og Drammen VVS AS | Drammen | 2026 |
| Oslo Og Follo Vedlikeholdsservice AS | Moss | 2012 |