Quantitative evaluation of molecular drag pumping action in turbopump channels allows an optimized placement of such channels among the stages of a high-compression hybrid turbine-type high-vacuum pumps. Although the drag action can be utilized in the entire range of pressures, the practical engineering considerations dictate the actual design (certain cross-section, length, parallel and series arrangement, and angular position) and placement of drag stages within the entire architecture of the pump which is to have a desired overall performance. The usual broad range of interest is between 0.1 and 100 torr but often can be more practical between 0.5 to 10 torr. Above 10 torr exit pressure, it is usually more effective to use other type of impellers. Theoretically, it may be desirable to have each stage of a hybrid turbopump of a different configuration but practical design (regarding size, ease of manufacture and assembly, and cost) necessitate some compromises. This is especially true of rotor design requirements. In addition, the choice of drag stage involves considerations of the wide range of pressure conditions in which a turbopump must function, the associated power requirements, and the crossing of various gas flow regimes. It is relatively simple to establish general guidelines for proper stage arrangements but actual design demands a complete knowledge of the performance of each individual impeller type.