Pre-ignition phenomena of methanol fuel (M85) and unleaded premium gasoline were studied with use of the post-ignition technique. The combustion pressure as well as a signal from the pre-ignition detector were analyzed. It was found that methanol fuel is more susceptible to pre-ignition compared to gasoline fuel. Large cycle-by-cycle variations are present with combustion by surface ignition at the time of pre-ignition. This was caused by wide variations in the 0% mass fraction burned point. Since ionization signals from the pre-ignition detector prior to spark ignition indicate the 0% mass fraction burned point by surface ignition, prediction of pre-ignition is possible with use of the post-ignition technique. Platinum tipped spark plugs were found to be highly susceptible to pre-ignition with methanol fuel.