Adiabatic burning velocities of premixed flat flames and propagation speeds of adiabatic cellular flames of mixtures of ethane + oxygen + carbon dioxide are reported. The oxygen content O-2/(O-2 + CO2) in the artificial air was varied from 26 to 35%. Nonstretched flames were stabilized on a perforated plate burner at I atm. A heat flux method was used to determine burning velocities 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 propagtion speed. Measurements in cellular flames are presented and compared with those for laminar flat flames and also with qualitative predictions of a theoretical model. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Cellularity disappears when the flames become only slightly subadiabatic. (C) 2003 The Combustion Institute. Published by Elsevier Inc. All rights reserved.