Bedrift O - Bygdøy
- Oros AS
- Osita AS
- Oneworld AS
- Opptun Eiendom AS
- Olbe Invest AS
- Ocm Eiendom AS
- Owners Holding AS
- Oslo Invest AS
- Oslo Seilforening
- Olsson Comms
- Orakel Holding AS
- Opdahl Consult
- Omega Ventures AS
- Oppdal Hyttegrend AS
- Olai Eiendom AS
- Ophaug Musikk
- Ohoy Holding AS
- Oslo Roklubb
- Ole Bil AS
- Oslo Seilforening
- Ole C. Mørch
- Oslo vest Invest AS
- Operasjonssykepleier Fredrikke Grimstad
- Oslo Base Invest AS
- Old Greenwich Holding AS
- Oslo Guide Harnes
- Oscharshall Slott Liv Bog
- Oslo Takst og bygg
- Oslo Politiets Selvbygglag Nr 10
- Ordo Sancti Constantini Magni (Ocm) Norge