Measurements of drop size characteristics of liquid-liquid coaxial swirl atomizers used in bipropellant rocket engines are made for a range of flow and geometric parameters. The merging and separation process of liquid sheets which exhibits hysteresis leads to a drastic variation in the size characteristics which will have serious implications on the engine throttling. At identical flow rates through a given coaxial atomizer, the merged state may result in mean drop size nearly 40-50% larger than that in the separated state. For constant inner flow rate, the Sauter mean diameter (SMD) of the combined spray initially increases, reaches a maximum, and thereafter reduces with the outer jet flow rate. The inner jet influences the drop size distribution only at low outer flow conditions. The atomization quality of the combined spray can be improved specifically at high outer flow rate conditions by increasing the swirl intensity of the jets or by providing a positive offset to the inner orifice.