Experimental studies of adiabatic cellular flames of CH4+O-2+CO2, C2H6+O-2+CO2, and C3H8+O-2+CO2 are presented. Visual and photographic observations of the flames were performed to quantify their cellular structure. Non-stretched flames of methane and propane were stabilized at atmospheric pressure on a perforated plate burner of improved design. New measurements are compared with recent results from this group. A Heat Flux method was used to determine propagation speeds under conditions when the net heat loss of the flame is zero. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Cellularity disappeared when the flames became only slightly sub-adiabatic. Increasing the oxygen content in the artificial air and increasing the temperature of the burner plate led to increase of the number of cells observed. No direct proportionality between the number of cells and propagation speeds in CH4+O-2+CO2 flames was observed. Dependence of the number of cells as a function of equivalence ratio clearly showed a local minimum in the stoichiometric mixtures.