This work examines the experimental assessment of the conditions required for sustainable autothermal catalytic combustion of mixtures of lean fuels (methyl ethyl ketone (MEK), acetone, propane, and methane) in a small nonadiabatic laboratory auto-cyclic reactor (ACR) loaded with a combination of laboratory-prepared monoliths and commercial palladium catalyst pellets. Despite the non-optimized physical parameters of this reactor, the experiments demonstrated that, for a given fuel, the domain of autothermal operation is dependent primarily on fuel/catalyst reactivity that, in turn, dictates the minimum heat output (power) requirement of the air/fuel mixture and, to a lesser degree, flow rate. In correlation with the reactivity of individual fuels, the power requirement for a flow rate of 64 L/min (ambient) increased, from 375 W for MEK and acetone to similar to 480 W for propane and 613 W for methane. For propane and methane combusted under the limiting conditions, oscillatory behavior was observed with the periods that correlated with the power of the fuel/air mixture. When the methane/air feed mixture was heated to 400 degrees C before entering the ACR, sustained combustion was assured for 0.6% methane flowing at a rate of 97.2 L/min.