- O’Neil & Associates, Inc.
- Oasis Transport Inc.
- Oasys International Corporation
- Oboyle Enterprises Inc [DBA Custom Machine]
- Obsidian Manufacturing Industries, Inc.
- Occupational Consulting, LLC
- Ocean Science Analytics
- Ohio Valley Archaeology, Inc.
- OIB Consulting Inc
- Okpro International LLC
- Olshesky Design Group, LLC
- Omaygah LLC
- Omni3 Partners, LLC
- ON SITE COLLECTION SVC
- On The Lot Events LLC [DBA OP 3]
- Onazry LLC
- One Aligned, Inc
- One Cow Standing, LLC
- One Mechanical Group LLC
- One Planet Corporation
- One Research and Development LLC
- One World Logistics Inc.
- Online Media Interactive, LLC
- Online Security Services Inc.
- Ontrend, Inc.
- Onyx Government Services, LLC
- Open Avatar Inc.
- Open System Sciences of Virginia, Inc.
- OpenFrame Technologies, Inc
- Opp Enterprise Inc
- Optimize Consulting, Inc.
- Optimizync LLC
- Optimum Environmental Corp.
- Optimum Performance & Strategic Consulting, LLC
- Optivor Technologies, L.L.C.
- Oratorio Inc.
- Orblogic Inc
- Orbis Technologies, Inc.
- Orvos Communications, LLC
- Osics, LLC
- OST, Inc.
- Outdo Wit Consulting Group, LLC
- Owen Medical Products, LLC
- Oxford Epidemiology Services LLC
- Oxford Government Consulting, LLC
- Oxygen, Respiratory & Medical Equipment, Inc