The American Petroleum Institute's base-oil group system (Groups I–V) defines refining quality and performance characteristics, but HTS classification of finished lubricants depends on the product's form, viscosity, and whether it is put up for retail sale or in bulk. A lubricant blended from Group III base oil is not automatically classified differently from a Group I blend — the HTS description governs, not the API group designation.

Finished lubricating oils and greases sourced from certain countries may be subject to Section 301 tariffs depending on origin and HTS classification. Importers should verify current Section 301 applicability for their specific product and country of origin with a licensed customs broker, as coverage and rates have evolved through successive USTR actions.