There are so many variables involved in an air or gas drilling situation that one general correlation has not been developed to predict appropriate volumetric requirements in the field. The results of previous attempts to calculate minimum volumetric requirement are valid over limited ranges of drilling conditions. This research has developed new empirical correlations for solids friction factors for sandstone, limestone, and shale. A new and more realistic technique for predicting minimum volumetric requirements is presented. This method includes a complete analysis of pressures throughout the system. It also offers flexibility in the selection of standpipe pressure and air flow rate, and thus, compressor specifications. The method is primarily graphical so that it can be used at the well site without access to a computer. Results are presented in tabular and graphical forms. These results confirm that existing methods may predict too low or too high a volumetric flow rate.