EPA RVP standards limit the volatility of gasoline sold during summer months (typically June 1 through September 15), which restricts butane blending into motor fuel during that period. As a result, butane import and storage activity tends to concentrate in the fall and winter, when blending restrictions ease and demand for heating and refinery feedstock use rises. Importers and traders should align supply contracts and storage arrangements with this seasonal pattern.

Both n-butane and isobutane are C4 hydrocarbons that fall within the liquefied butane SITC heading, but they are chemically distinct isomers with different refinery and petrochemical applications. At the HTS level, US tariff schedules may distinguish between them at the 10-digit level. Importers should specify the isomer in commercial documentation and confirm the applicable HTS subheading with a licensed customs broker to ensure correct classification.