The efficiency of a combustion system is affected by the stability of the combustion. The behaviour of a system composed of a combustion chamber is governed by the following basic variables: (a) flow of air and fuel, (b) flame characteristics, (c) system geometry. Each of the above variables can have an active effect on the instability of the system. To achieve and maintain combustion instabilities, their origin and characteristics must be explored. To define, characterize and then minimize such instabilities, the following problems must be investigated: (a) the effect of the excited system parts on the total response of the system, (b) the generation of instabilities by the flame and recirculation into the feedback system, (c) the effect of flame length on the instabilities, (d) the effects of gas chamber volume on instabilities. The components of the system can be excited by altering one or a combination of any of the basic system variables. Hence, by investigating the effect of these variables one can determine, to an acceptable level of accuracy, the behaviour of the system. Investigation of the last three problems also includes problem (a). The present report is primarily concerned with the investigation of (b), (c) and (d). Experiments were conducted and dynamic measurements made to determine the influence of recirculation, time bag and gas chamber volume on the instability of the system. Results indicate that it is possible to predict the extent of the instabilities. The following changes were found to increase stability: (1) decrease of the recirculation in the combustion chamber (the best method to achieve this decrease appears to be to decrease the diameter of the combustion chamber), (2) decrease of the volume of the fuel chamber, (3) decrease of the time lag of the reactions. The investigation shows that in industrial burners, the stability of the combustion system requires that the following points should be observed during design: (1) swirters of the burners should be moveable axially, (2) pressure in the gas lance should be high compared with the combustion chamber pressure, (3) sheddings of vortices must be avoided.