Down-hole drilling motors have long been used for special drilling problems but use of turbines has not yet proved to be economical for a wide range of drilling applications. A recent Shell Oil Co study is aimed at providing the answer to this and other questions about the potential of turbodrilling. This article, first of a three-part series detailing research and testing involved in the Shell study, cites the advantages of diamond bit-turbine drilling and the requirements for an effective diamond-bit design, and describes the needed performance characteristics for the turbines.