Gas chromatography (GC) compositional analysis reports are the primary supporting document, showing the percentage breakdown of each component in the stream. Importers should also retain the product's safety data sheet (SDS), the supplier's product specification sheet, and any relevant refinery or processing records that explain why the mixture does not qualify under a more specific heading. Customs authorities may request these documents during a post-entry audit or CF-28 inquiry.

Mixed C4 raffinate streams from steam crackers (after butadiene extraction), liquefied refinery gas blends containing varying proportions of propane, butane, and pentanes, and specialty hydrocarbon mixtures used as aerosol propellants or refrigerant blends are typical examples. The NES designation applies when the mixture's composition prevents classification under a single named-component heading, making compositional documentation essential for both classification and valuation purposes.