The determination of the minimum fuel octane required for an aircraft engine, utilizes detonation equipment and test techniques developed prior to World War II. These procedures were designed to provide a 12% margin of safety on traditional leaded aviation fuels which met the lean and rich ratings as listed in the applicable ASTM specification. Now, due to a possible phase out of leaded fuels, it appears necessary for aircraft engine manufacturers and STC applicants to re-evaluate these techniques and procedures to determine if they are applicable for unleaded fuels. And to re-evaluate existing engines to determine the minimum acceptable requirements for a new unleaded aviation gasoline. This paper reviews these techniques and looks at possible requirements for an unleaded aviation gasoline.