ABSTRACT A performance model for Polycrystallíne Diamond Compact (PDC) bits has been modified to include the wear prediction of individual cutters. Wear predictions are based on the geometry of each cutter, the rock, type, the forces acting on the cutter, cutter velocity, and cutter temperature. The results of predicted and actual cutter wear for different 8-1/2 in. field worn PDC bit designs are shown. The worn geometry of each cutter was measured and compared to the model's prediction. Laboratory performance tests were also conducted with similar bit designs to quantify the effect of bit imbalance. Reduced ROP, drilling an overgage hole, and increased cutter wear and breakage can be the result of bit imbalance.