ABSTRACT It is highly desired to develop a simple and reliable method for determining the air volume requirements for directional air drilling operations. Using Niku-radse's friction factor correlation for turbulent air flow, Angel's empirical model for determination of air volume requirements for vertical well drilling is modified and extended to deviated and horizontal well drilling. The new model is verified by field data taken from air drilling operations. The result given by the this model matches Amoco's experience very well in a wide range of well geometry for vertical wells. A series of charts which are similar to Angel's is presented for quickly determining circulation rates for vertical and directional air drilling operations.