A series of 36 laboratory drilling tests were conducted to study the mechanics of diamond coring in rocks. The drillability of a surface-set drill bit was assessed based on the penetration rate, applied torque, and specific kerfing energy. Factors governing efficiency of the diamond core drilling included wight-on-bit, core bit rotational speed, and rock types.Results of the experiment indicated that penetration rate and applied torque of the drilling increased exponentially as the weight-on-bit increased. However, the specific kerfing energy decreased as the weight-on-bit increased. The effect of rotational speed of the bit on the penetration rate was found to be significant. An exponential relationship between the penetration rates and the uniaxial compressive strengths of rock samples was noted.