| 635.99 | Oars, wooden | |
| 048.14 | Oats, clipped, whether or not pearled | |
| 048.14 | Oats, hulled, whether or not sliced or kibbled | |
| 048.14 | Oats, kibbled | |
| 048.14 | Oats, pearled | |
| 048.11 | Oats, roasted or swollen as breakfast food, ready for consumption | |
| 048.13 | Oats, rolled or flaked (excl. prepared breakfast foods) | |
| 045.2 | Oats, seed | |
| 045.2 | Oats, unmilled | |
| 884.32 | Objectives (incl. polarizing) for astronomical instruments, binoculars, refracting telescopes, microscopes | |
| 898.23 | Oboes | |
| 663.52 | Obsidian, expanded or exfoliated | |
| 667.31 | Obsidian, precious, unworked or simply sawn or roughly shaped, whether or not graded, not strung, mounted or set | |
| 667.39 | Obsidian, precious, worked other than simply sawn or roughly shaped, whether or not graded, not strung, mounted or set | |
| 898.23 | Ocarinas | |
| 287.99 | Ochre, bismuth (bismuth ore) | |
| 278.99 | Ochres (earth colours), whether or not calcined or mixed together or with other earth colours (excl. bismuth ochre) | |
| 513.79 | Oct-1-yne-carboxylic acid | |
| 511.39 | Octachloronaphthalene | |
| 511.39 | Octachlorotetrahydro-4,7-endomethyleneindane | |
| 511.39 | Octachlorotetrahydromethanoindane | |
| 512.19 | Octadecan-1-ol | |
| 511.19 | Octadecane | |
| 513.73 | Octadecyl methacrylate | |
| 511.39 | Octafluorocyclobutane | |
| 515.5 | Octamethylcyclotetrasiloxane | |
| 514.89 | Octamethylpyrophosphoramide (OMPA) | |
| 515.5 | Octamethyltrisiloxane | |
| 512.14 | Octan-1-ol | |
| 516.21 | Octanal | |
| 874.25 | Octane index-measuring appliances for laboratories | |
| 511.14 | Octanes | |
| 513.79 | Octanoic acid and its salts and esters | |
| 512.14 | Octanol | |
| 874.11 | Octants | |
| 515.75 | Octaverine (INN) | |
| 511.19 | Octenes, not less than 95% pure | |
| 513.77 | n-Octoic (caprylic) acids and their salts and esters | |
| 036.37 | Octopus, frozen, dried, salted or in brine | |
| 036.33 | Octopus, live, fresh or chilled | |