Octane is the most important property in gas.

A gasoline octane rating measures the fuel’s ability to resist auto-ignition (combustion of the air: fuel mixture before desired). Auto ignition can cause noise in the engine and, in some cases, harm the engine.  A higher octane-rating resists auto-ignition and permits engine designers to make more efficient and more powerful engines.

Increasing the octane rating of gasoline allows for improved engine efficiency, fuel consumption, and decreased greenhouse gas emissions by allowing higher compression ratios and other efficient power plant designs, such as downsizing, down speeding, cylinder deactivation and hybridization. Octane rating has become the most limiting factor in achieving new efficiency and environmental objectives for gasoline powered vehicles. When America designs a fleet around a higher-octane standard, it will result in fleet-wide energy efficiency improvements, lower harmful emissions, lower greenhouse gas emissions and better performance.