Results of measured adiabatic burning velocities of methane- and propane-air premixed laminar flames are presented, as obtained by the Heat Flux method. A comparison is made with results of the Counterflow method. The effect on the Counterflow method results of a non-linear instead of a linear correction for stretch is estimated. With a non-linear correction the agreement between both methods is good. It can be concluded that non-linear correction for stretch on the results of the Counterflow method is necessary in general. However, its effect may vary with varying fuel gas.