Abstract Advancements in tools and technology for air drilling have been quite numerous. One of the more publicized tools in recent years has been the air-rotary-percussion drill. This paper is prepared to evaluate the tool performance and to indicate problem areas where the tool may be used to the greatest economical advantage. Continued improvement of the tool, along with improved bit design, will extend the application of air-rotary-percussion techniques to greater hole intervals in oil and gas wells. Introduction Percussion drilling, as used in the oil field today, is a combined action in which positive rotation of the tool together with a high static thrust on it has been superimposed on the basic percussive action. The percussive action is a process of rock drilling in which repeated blows are applied to the surface of a rock through a pointed bit as used in cable tool drilling. One of the most successful ways of drilling a hardrock formation, this method has been improved recently by the percussive rotary technique. The tool is installed next to the bit and is actuated by air the circulating media. The volume of air and the pressure requirements of the percussion tool are designed to be compatible with air drilling equipment currently being used Due to the greater penetration rate of the down-hole machine, the volume of air required to remove all the cuttings from the annulus is sometimes 20 per cent greater than conventional rotary air drilling. Air not consumed in the operation of the machine is directed through the bit for bottom-hole cleaning while the used air is discharged at or near the bit, thus giving total hole-cleaning capacity. The pressure required to operate a percussion tool varies with the individual tool. Some tools operate with as little as 50 psi, while others require as much as 200 psi, with their maximum efficiency at 400 psi. The percussion tool advances by punching rather than by boring under pressures; therefore, its progress is more nearly vertical while drilling in hard, slanting formations. The tool also maintains a higher penetration rate without the excessive hole deviation sometimes encountered in conventional air drilling. Some percussion tools with heavy impacts have a tendency to destroy the standard-type bits; therefore, this requires that the manufacturers "beef-up" their bits with reinforced seam welds to withstand the excessive blows.