Bedrift O - Mjøndalen
- Omnicon
- Optimumcar AS
- Onto AS
- Osbakken Idrettslag
- Oma Security AS
- Olsen Tore
- Olsen Thomas
- Oslo AS Monsterbedriften
- Olaf Nordalen
- Olsen Utilitarianism
- Ohldieck Ufv
- Olsen Plastgjennvinning
- Olsen Catering AS
- Oak Invest AS
- Overskeid Fysioterapi
- Orfs Invest AS
- Optimus Invest AS
- Open White AS
- Omnicon Norge AS
- Otterstrom Racing AS
- Optima Wood AS
- Otto Ressurs AS
- Orlund Holding AS
- Opdahl Blomster
- Ohm Byggtek
- Ola Foss Eriksen
- Optima Wood Bjurulf
- Ole-Jonny Vigdal
- Ole Alexander Andersen
- Olaf Johannes Thomassen
- Orapan Beauty Nordby
- Olsen på Hjørnet
- Ot Bil Oddvar Tuften
- Osoble Tur og Transport
- Olibuss Transport Pawel Glowacki
- O.C.Rygh Eiendom V/Ole Christian Rygh
- Opplæringskontoret for Bygghåndverksfag i Viken (OB Viken)