Bedrift O - Kjeller
- Omeragic
- Oncogene AS
- Oddvar Hagen
- Oks Eiendom AS
- Oseberg Capital AS
- Osa Agenturer
- Oslo Flyveklubb
- Oslo Liftutleie
- Opdal Design
- Oks Friskole
- Oks friskole
- Omar Ørn Jonasson Enk
- Oslotak Edgaras Zvinys
- Odd Normann Holding AS
- Oslo Tømrer Ghorbani
- O-Con - Otnes Consulting
- Oslomet - Storbyuniversitetet Studiested Kjeller
- Oslo Kristne Senter (OKS)
- Out for A Hero Holding AS