|
| 7230 | Optical scanning data services | |
| 3312 | Optical test and inspection equipment, manufacturing | |
| 5239 | Opticians, retail | |
| 3210 | Optoelectronic devices, manufacturing | |
| 3311 | Optometers, manufacturing | |
| 5139 | Optometric equipment and supplies, wholesale | |
| 9112 | Optometrists' associations | |
| 8519 | Optometrists' offices | |
| 8519 | Optometrists, offices and clinics of | |
| 2423 | Oral contraceptive preparations, manufacturing | |
| 5139 | Oral hygiene products, wholesale | |
| 8512 | Oral pathologists, offices of | |
| 8512 | Oral surgeons, private practice | |
| 0113 | Orange groves and farms | |
| 1513 | Orange juice concentrates, frozen, manufacturing | |
| 5520 | Orange juice stand | |
| 1513 | Orange juice, fresh, manufacturing | |
| 2429 | Orange oil, manufacturing | |
| 5149 | Orchard care chemicals, wholesale | |
| 0140 | Orchard cultivation services | |
| 0140 | Orchard fruit picking, hand | |
| 7414 | Orchard management and maintenance, with or without crop services | |
| 0140 | Orchard spraying and dusting service (except from aircraft) | |
| 9214 | Orchestras | |
| 3692 | Orchestrions, manufacturing | |
| 5251 | Order taking offices of mail-order houses, retail | |
| 2927 | Ordnance, military, manufacturing | |
| 2924 | Ore crushing, washing, screening and loading machinery, manufacturing | |
| 5150 | Ore dressing machinery, wholesale | |
| 4520 | Ore milling and metal processing plants, construction | |
| 3692 | Organ parts and materials (except organ hardware), manufacturing | |
| 3692 | Organ parts and materials, manufacturing | |
| 5260 | Organ repair (including tuning) | |
| 5260 | Organ tuning and repair | |
| 5149 | Organic chemicals, synthetic, wholesale | |
| 2430 | Organic fibres and filaments (except cellulosic), manufacturing | |
| 2411 | Organic pigments, dyes, lakes and toners, manufacturing | |
| 7414 | Organization development consulting services | |
| 9900 | Organization for Economic Co-operation and Development | |
| 7414 | Organization management consultants | |
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