This work presents and validates a new methodology that determines the adiabatic ignition delay of a hydrocarbon-based fuel using several nonadiabatic ignition delay measurements. The new methodology was developed and validated in a numerical modeling and then applied to propane autoignition experiments to determine the adiabatic ignition delay of the fuel, the so-called measured adiabatic ignition delay. Propane ignition delays were measured in a wide range of low to intermediate gas temperatures ranging from 769 to 952 K, at pressures of 23-30 bar, and at equivalence ratios of approximately 0.5 and 1.0 for a rapid compression machine (RCM). Application of the new methodology removed the effect of heat transfer on measured ignition delay, thus reporting the adiabatic ignition delay free from facility heat-transfer effects. The measured adiabatic ignition delays from the RCM are close to the ones measured by a shock tube.