Recent studies have indicated that small changes in concentration of higher hydrocarbons in natural gas can severely reduce ignition delay times of methane-based fuels. To increase the database of autoignition delay times for methane-based fuel mixtures characteristic of natural gas, experiments to measure autoignition delay times have been performed for a variety of gaseous fuels in an atmospheric flow reactor. Autoignition delay times were measured for pure fuels in air including methane, ethylene, ethane, and propane. The effect of higher hydrocarbon addition on methane-based fuel ignition delay was then investigated for fuel mixtures composed of methane/ethylene, methane/ethane, and methane/propane where methane composition varied from 25-95% by volume. Autoignition delay times were also measured for multi-component methane-based fuels composed of methane/ethane/propane and air. Finally the effect of CO ₂ addition on methane autoignition was investigated. For all experiments, Φ ranged between 0.5 and 1.25 and temperatures ranged from 931 K to 1137 K. The measurements made in this study will benefit the combustion community by both providing valuable insight into the effects of additives on methane ignition as well as validation data for chemical kinetics mechanisms for predicting ignition of methane-based fuels.