According to the EPA 61 FR 3832 - Prohibition on Gasoline Containing Lead or Lead Additives for Highway Use
EPA has historically defined unleaded gasoline as gasoline that is produced without the use of any lead additive and that contains no more than 0.05 gram of lead per gallon. EPA interprets section 211(n) this way for the following reasons. The regulatory definition of ``unleaded gasoline’’ also contains a cap on the amount of phosphorus, see 40 CFR 80.2(g), but the phosphorus cap is not relevant to the discussion of section 211(n). Unleaded gasoline that was produced without lead additives may pick up trace amounts of lead as it passes through refinery and transport systems that had previously contained leaded gasoline.
This is the same limit Formula 1 has for its fuels. Formula 1 fuel is unleaded fuel.