Summary Shell Canada Ltd. has air-percussion drilled 48 wells since Fall 1983. The industrial hammer was used predominantly, but the older oilfield hammer was used occasionally. A total of 117 solid-head bits were run. Experiences with the industrial percussion hammer indicated that tool modifications were required to reduce hole spiraling and the tendency of bits to go undergauge. High penetration rates (ROP's) with the new hammer required excessive blowing on connections, leading to the modification of a computer program for air-volume requirements. Because minor equipment failures were causing lost time, modifications were made to the jet system, sample catcher, and downhole floats.