USAI focuses on US and Canadian midstream energy infrastructure companies that derive the majority of their revenue from the processing, transportation and storage of oil, natural gas and refined products. Holdings are selected by market cap and separated into two fixed-weight categories based upon legal structure: US & Canadian midstream companies (80%) and US midstream MLPs (20%). Holdings within each category are weighted by market cap. Because less than 25% of USAIs holdings are taxed as partnerships, it avoids the tax issues faced by many competitors in the MLP space. The index is rebalanced on a quarterly basis.