Bedrift O - Mjøndalen
- Onto AS
- Omnicon
- Optimumcar AS
- Omnicon Norge AS
- Olaf Haug
- Osiadacz Anna
- Olaf Nordalen
- Olsen Thomas
- Olsen Tore
- Oslo AS Monsterbedriften
- Oma Security AS
- Oak Invest AS
- Olsen Catering AS
- Optimus Skadedyrkontroll AS
- Open White AS
- Oma Security AS
- Optimus Invest AS
- Otto Ressurs AS
- Optima Wood AS
- Ohldieck Ufv
- Olsen Plastgjennvinning
- Otterstrom Racing AS
- Opdahl Blomster
- Orfs Invest AS
- Osbakken Idrettslag
- Olaf Johannes Thomassen
- Ola Foss Eriksen
- Optima Wood Bjurulf
- Onkel Marcin - Sadokierski
- Ole-Jonny Vigdal
- Olsen på Hjørnet
- Osoble Tur og Transport
- Ot Bil Oddvar Tuften
- Olibuss Transport Pawel Glowacki
- Opplæringskontoret for Bygghåndverksfagene i Buskerud (OBU)
- O.C.Rygh Eiendom V/Ole Christian Rygh