3811.11 - Based on lead compounds:

This HTS category, 3811.11, specifically covers antiknock preparations designed to enhance the octane rating of fuels, primarily gasoline. These preparations work by increasing a fuel's resistance to knocking or pinging during combustion, which is essential for engine performance and longevity. The key characteristic for classification under this heading is the presence of lead compounds as the active ingredient in these fuel additives.

While the broader heading 3811 encompasses various prepared additives for mineral oils and similar liquids, this subcategory focuses solely on antiknock preparations. It is distinguished from its sibling category, 3811.19.00.00 (Other), which covers antiknock preparations not based on lead compounds, such as those utilizing organic compounds like methylcyclopentadienyl manganese tricarbonyl (MMT). Therefore, the presence or absence of lead compounds is the critical differentiator.

Within this category, further subdivisions exist to refine classification. Subcategory 3811.11.10.00 specifically addresses preparations based on tetraethyl lead or a mixture of tetraethyl lead and tetramethyl lead, which were historically the most common lead-based antiknock agents. The remaining preparations within this lead-based segment are classified under 3811.11.50.00 (Other), capturing any other antiknock preparations utilizing lead compounds but not falling into the specific tetraethyl lead-based definition.