The continuously stirred tank reactor (CSTR) technique is applied toequimolr acetaldehyde oxygen mixtures across a wide range of vessel residence times. Heat release curves are obtained in each case in the regions where stable steady state exists. In the regions of oscillatory cool flames the steady state is unstable and cannot be obtained experimentally. The oscillatory region always contains part of the region of negative temperature coefficient, as expected on theoretical grounds. At very short residence times a new effect is shown in this system, i.e., a discontinuous transition from the familiar type of cool flames to flames with quite different amplitude, frequency, and shape. In the immediate region of this bifurcation the system shows "indecision" or interspersed flames of each type for a short period. The reverse transition occurs at quite a different ambient temperature, showing hysteresis of as much as 25K. A tentative qualitative description of the nature of this bifurcation is given.