OAC
- Acetoxy group
- Ayn Rand Institute
- Ayn Rand Institute
- Oakland Coliseum Station
- Object Action Complex
- Ocean Affairs Council
- Ohio Arts Council
- Ohio Athletic Conference
- Olivetolic acid cyclase
- On Athletics Club
- One America Committee
- Online Archive of California
- Ontario Academic Credit
- Ontario Agricultural College
- Ontario Arts Council
- Oral anti-coagulant
- Orange Association Canada
- Orange Order
- Orthodox Anglican Church
- Orthodox Anglican Communion