- Obee's Soup Salad Subs
- Oberweis Dairy
- OBIE Media
- Oboz
- O'Brien & Associates
- O'Brien & GERE Engineers
- O'Brien Realty
- Obstetrics & Gynecology
- Occhiali Da Sole
- Occupational Development Center
- Occupational Health & Rehabilitation
- Occupational Medicine
- Ocean Beauty Seafoods
- Ocean Nails
- Ocean National Bank
- Ocean Spray Cranberries
- Ocean State Job Lot
- Oce'-usa
- O'Charley's
- O'Connell Convenience Plus
- O'Connor & Associates
- O'Connor Michael J & Associates
- Odd Fellows
- Odd Fellows Lodge
- Odd Fellows Temple
- Odds & Ends
- Odyssey
- Odyssey Travel
- Off Broadway
- Off Broadway Shoe Warehouse
- Off Broadway Shoes
- Off the Beaten Path
- Off the Grill
- Off the Hook
- Off the Rack
- Off the Top
- Off The Wall
- Off Track Bedding
- Office Bar