ABSTRACT For the past few years the industry has been trying to extend the operating range of polycrystalline diamond compact (PDC) bits in terms of formations that can be drilled. Initially, the direction was uphole to the softer formations where the high standoff blade bits and large diameter PDC bits have proven economic. The next step is to extend downhole where the formations are harder and generate more heat. Typically, either tungsten carbide insert (TCI) bits or natural diamond bits are used in these harder formations because the heat degrades the polycrystalline diamond compact cutters. However, insert bits tend to be short-lived and require tripping more often than is satisfactory and diamond bits have penetration rates that are slower than desirable. Bits using PDC cutters with enhanced thermal stability and a radius of curvature on the diamond table have demonstrated a significant economic impact in many harder formations. The diamond wafer is shaped like a dome and set in the bit in place of the conventional, flat PDC cutters. The dome shape dissipates heat better, facilitates more efficient mechanical cuttings removal and drills with a constant rate of penetration throughout the life of the cutter due to the variable rake angle. In addition to extensive laboratory testing, a rigorous field-test program was undertaken to determine the significance of this new development. Field-test results are presented from Northern Europe and the lower Wilcox Frio sands and other formations of South Texas.