The drilling rate index (DRI) is an important parameter that influences the drillability of rocks. It can easily be used when estimating the economics of any excavation operation. Therefore, in the current study, an attempt was made to investigate the rock properties that govern the DRI. The relationships between the DRI and some physicomechanical rock properties were investigated based on data obtained from experimental work and in situ studies performed in different tunnels. Regression analysis was employed to develop models for estimating the DRI based on physicomechanical rock properties. The derived models were verified based on the behavior of the determination coefficient, the t test, and the F test. The study showed that the DRI decreases with increasing uniaxial compressive strength, point load strength, Brazilian tensile strength, and Schmidt rebound hardness. It was also concluded that the DRI increases with increasing apparent porosity and void ratio. Additionally, modeling results revealed that the proposed models can be successfully used as tools to forecast the DRI.