| OA | OB | OC | OD | OE | OF | OH | OI | OK | OL | OM | ON | OP | OR | OS | OT | OU | OV | OX | OY | OZ |
| Index entry | NAICS Code | U.S. NAICS Title |
|---|---|---|
| Obedience training services, pet | 812910 | Pet Care (except Veterinary) Services |
| Oboes manufacturing | 339992 | Musical Instrument Manufacturing |
| Observation towers | 713990 | All Other Amusement and Recreation Industries |
| Obstetrical hospital | 622310 | Specialty (except Psychiatric and Substance Abuse) Hospitals |
| Obstetricians' offices (e.g., centers, clinics) | 621111 | Offices of Physicians (except Mental Health Specialists) |
| OA | OB | OC | OD | OE | OF | OH | OI | OK | OL | OM | ON | OP | OR | OS | OT | OU | OV | OX | OY | OZ |