The Phillips Small Sample Octane Number (SSON) Methods (Research and Motor) were developed from the ASTM methods by replacing the ASTM fuel metering system with a variable stroke positive displacement metering pump, the fuel selector valve with an automatic valve, and by using digital signal processing procedures. The pump, fuel sampling, and signal processing are under computer control. Important features include direct comparison of each test fuel with two primary reference fuels, signal averaging to enhance signal-to-noise ratio, and digital recording of the transducer output before processing. The transducer used is a standard D1 pickup which produces a voltage that is proportional to the rate-of-change of pressure within the engine cylinder.This report describes the application of SSON techniques to the determination of Motor octane Numbers (MON), and compares SSON results directly to ASTM results. The SSON method takes only six minutes and requires a twenty ml sample of test fuel. The standard ASTM method takes twenty to twenty-five minutes and 400 ml of test fuel.