A brief summary of the previous experimental studies on the ignition of methane in shock tubes is given by way of introduction. The ignition delay characteristics of methane-oxygen mixtures highly diluted with argon were studied behind reflected shock waves. Ignition was identified by pressure rise and visible light emissions using piezoelectric transducers and photomultiplier detection respectively. The measurements covered a temperature range of 1600-2100 K and a pressure range of 1 to 6 atm. The equivalence ratio was varied from 0.2 to 5.0. The following expression