A study of spray formation in a pneumatic nozzle With external mixing is pre- sented. The mast importent parameters are highlighted and their influence on the mean drop diameter and size distribution is examined. A theoretical approach is outlined which yields several exponential models containing all important parame- ters in dimensionless form. The most appropriate model for drop size prediction is recommended after experimental verification and comparison with several previously published models. Special attention was paid to development of s simple model which makes its practical application easier.