Abstract: A rotary drag-type drill bit, for drilling holes in subsurface formations, comprises a bit body having a leading face and a gauge region, a number of blades formed on the leading face of the bit and extending outwardly away from the axis of the bit so as to define between the blades fluid channels leading towards junk slots in the gauge region. Cutting elements are mounted along each blade, and nozzles in the bit body supply drilling fluid to the leading face of the bit for cleaning and cooling the cutting elements. At least some of said blades each have a leading edge which is non-linear, or convexly or concavely curved, as viewed axially of the bit, as it extends outwardly away from the axis of the bit. Blades of different shapes may be located alternately around the axis of the bit. The junk slots at the gauge region, and the kickers between which they are formed, may vary in width around the periphery of the bit, and may be inclined to the axis of the bit.