- Office Supplies, Equipment & Office Furniture Stores, Sykesville
- Oil Change & Lubrication, Sykesville - Auto Oil & Quick Lube
- Oil Extraction Downhole, Sykesville
- Oil Industry & Oil Field Equipment & Services, Sykesville - Oil Companies
- Ophthalmologists, Sykesville - Eye Doctors, Physicians & Surgeons (Ophthalmology)
- Optical Stores - Eyeglasses, Lenses & Sunglasses, Sykesville
- Opticians, Sykesville
- Optometrists, Sykesville - Eye Doctors, Physicians & Surgeons (Optometry)
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- Ornamental Nursery, Sykesville
- Ornamental Nursery Services, Sykesville
- Orthodontist, Sykesville - Teeth Straightening, Invisalign & Dental Braces
- Other Building Materials & Supplies, Sykesville
- Other Specialties, Sykesville - Doctors, Physicians & Surgeons
- Outdoor & Lawn & Garden Equipment Repair & Service, Sykesville
- Outdoor Equipment & Accessories, Sykesville
- Outdoor Furniture & Patio Furniture, Sykesville - Garden Furniture Stores
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