Eight shallow (30-foot-deep) holes were drilled in four formations to determine if the reduction in penetration rate that usually occurs when air drilling is changed to mist drilling might be due to the physical action of drilling a wet, soapy rock. The results showed an average loss of 9.3%, with the greatest loss occurring in limestone. The softest formation (claystone) showed only a 1.2% reduction in penetration rate; the two sandstones averaged 10.0-percent loss; and the limestone showed a significant 15.8% loss. This indicates that the loss of penetration rate due to wetting the rock while mist drilling is small but would be significant when drilling a long interval. The findings indicate that when drilling hard rocks at the surface with mist instead of air, a penetration rate loss of approximately 12% (compared to the drilling rate with air) will occur due to the effect of jetting the soapy water through the bit onto the formation being drilled.