The blowout limits of a methane diffusion flame in a co-flowing air-fuel or air-diluent stream were determined for a range of surrounding co-flow stream velocities, both laminar and turbulent, up to ~ 1.50 m/s. Methane, ethylene, propane and hydrogen were used as the fuels in the surrounding co-flow stream while nitrogen and carbon dioxide were used as diluents. The experimental results show that the velocity of the surrounding stream affects the blowout phenomena significantly. An increase in the stream velocity has a detrimental effect on the blowout limits at very low velocities up to 0.30 m/s (essentially laminar flow) and at velocities higher than 1.50 m/s (turbulent flow). The addition of a fuel to the air stream in most cases enhances the blowout limit of a methane diffusion flame. However, different trends in the variation of the blowout limits with the surrounding fuel concentration were observed, depending on the type of fuel used and on whether the surrounding coflow stream was laminar or turbulent. The addition of nitrogen or carbon dioxide to the air stream results in decreasing the blowout limits. The effect is more severe at the higher velocities.