Subheading 381121 covers additive packages that themselves contain petroleum or bituminous mineral oils as a component, while 381129 covers lubricating oil additives formulated without such oils. The distinction turns on the composition of the additive package itself, not the oil it will be blended into. A certificate of analysis or material safety data sheet identifying the carrier medium is typically needed to support classification.

Lead-based antiknock preparations (tetraethyl lead and similar compounds) are effectively banned from use in on-road fuels in the United States and most major markets, so commercial import volumes under 381111 are negligible. The subheading remains in the tariff schedule but is rarely used in practice. Non-lead antiknock preparations under 381119 are the commercially active subheading.