During the past 4 yr, the U.S. Bureau of Mines has investigated the use of chemical additives in drilling fluids to enhance drilling performance. Laboratory diamond-impregnated core drilling tests were performed on Sioux quartzite, Westerly granite, Minnesota taconite, and Tennessee marble using various concentrations of inorganic salts, cationic surfactants, and cationic polymers as well as the nonionic polymer, polyethylene oxide (peo), as the drilling fluid. In these tests it was found that maximum penetration rate improvements ranging from 60 to 650 pct and simultaneous maximum bit life improvements ranging from 60 to 400 pct were obtained when the condition of zero surface charge (zsc) on the rock drilled was met. Peo was found to be the best additive as it not only produced the highest improvements in drilling performance under zsc conditions but could maintain the zsc condition over a wide range of concentrations, not just at a single concentration like the cationic additives. Field rotary tricone drilling tests on Minnesota taconite using a combination of air and a mist of the zsc concentration of peo solution as the drilling fluid resulted in a 72- pct increase in penetration rate and a simultaneous 26-pct increase in bit life. Field diamond core drilling of granite with zsc concentrations of polyethylene oxide solutions produced increases in bit life of 100 to 350 pct. Cost savings associated with enhanced drilling performance are also discussed.