| 8511 | Orthopaedic hospitals | |
| 8512 | Orthopaedists, private practice | |
| 5231 | Orthopedic and artificial limb stores-retail | |
| 3311 | Orthopedic braces (spinal, cervical, leg and knee), manufacturing | |
| 3311 | Orthopedic canes, manufacturing | |
| 3311 | Orthopedic devices and materials, manufacturing | |
| 5139 | Orthopedic equipment, wholesale | |
| 3311 | Orthopedic extension shoes, manufacturing | |
| 3311 | Orthopedic hosiery, elastic, manufacturing | |
| 8511 | Orthopedic hospitals | |
| 8512 | Orthopedic physicians, offices of | |
| 2694 | Orthopedic plaster, gypsum, manufacturing | |
| 1920 | Orthopedic shoes (except extension shoes), men's, manufacturing | |
| 3311 | Orthopedic supplies, manufacturing | |
| 3311 | Orthopedic supports, manufacturing | |
| 8519 | Orthotherapists | |
| 5231 | Orthotic devices, retail | |
| 2021 | OSB (oriented strandboard), manufacturing | |
| 3312 | Oscillators (e.g., instrument type audiofrequency and radiofrequency), manufacturing | |
| 3312 | Oscilloscopes, manufacturing | |
| 0111 | Osier growing | |
| 1320 | Osmium mining | |
| 3312 | Osmometers, manufacturing | |
| 2429 | Ossein, manufacturing | |
| 8512 | Osteopathic physicians, offices and clinics of | |
| 8512 | Osteopaths' offices | |
| 8519 | Osteoperosis centres | |
| 5150 | Ostomy supplies, wholesale | |
| 0122 | Ostrich farming | |
| 4520 | Other structural and related work | |
| 3311 | Otoscopes (except electromedical), manufacturing | |
| 3311 | Otoscopes, electromedical, manufacturing | |
| 0500 | Otter trawling | |
| 5239 | Outboard motor dealers, retail | |
| 2911 | Outboard motors (except electric), manufacturing | |
| 3190 | Outboard motors, electric, manufacturing | |
| 5150 | Outboard motors, wholesale | |
| 9249 | Outdoor adventure operations (e.g., white water rafting), without accommodation | |
| 5510 | Outdoor adventure retreats (with accommodation) | |
| 7430 | Outdoor display advertising services | |