E85 is an abbreviation for an ethanol fuel blend of 85% denatured ethanol fuel and 15% gasoline or other hydrocarbon by volume, although the exact ratio of fuel ethanol to hydrocarbon can vary considerably while still carrying the E85 label. The ethanol content is adjusted according to the local climate to maximize engine performance. ASTM 5798 specifies the allowable fuel ethanol content in E85 as ranging from 51% to 83%.