- OI Partners
- Oil Can Henry's
- Oil Exchange
- Oilily
- Oilind Safety
- OK Auto Sales
- OK Barber Shop
- OK Cleaners
- OK Corral
- O-K Paper Center
- Ok Tire Store Saskatoon
- Oklahoma Cardiovascular Associates
- Oklahoma County Senior Nutrition Program
- Oklahoma Farmers Union
- Oklahoma Farmers Union Insurance
- Olan Mills
- Olan Mills Portrait Studio
- Olan Mills Portrait Studios - in Kmart
- Olan Mills Portrait Studios - Kmart
- Olan Mills Portrait Studios - Studio
- Old American Insurance
- Old Chicago
- Old Country Bakery
- Old Country Buffet
- Old Country Store
- Old Dominion Freight Lines
- Old Glory
- Old Home Bread
- Old Kent Bank
- Old Kent Mortgage
- Old Mexico
- Old Mexico Restaurant
- Old Mill
- Old National
- Old National Bank
- Old Navy
- Old Navy Clothing
- Old Navy Clothing Company
- Old Republic National Title Insurance Company