This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
6 different classes according to location and/or season.
As gasoline is distilled, the temperatures at which various fractions are
evaporated are calculated. Specifications define the temperatures at which
various percentages of the fuel are evaporated. Distillation limits
include maximum temperatures that 10% is evaporated (50-70C), 50% is
evaporated (110-121C), 90% is evaporated (185-190C), and the final boiling
point (225C). A minimum temperature for 50% evaporated (77C), and a maximum
amount of Residue (2%) after distillation. Vapour pressure limits for
each class ( 54, 62, 69, 79, 93, 103 kPa ) are also specified. Note that the
EPA has issued a waiver that does not require gasoline with 9-10% ethanol to
meet the required specifications between 1st May - 15 September.
 
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