The radial-outflow reaction turbine, a pure-reaction turbine designed to improve the conversion efficiency of geothermal energy into electrical power is described. It also has potential as a total-flow turbine for low-temperature water. The principle of incomplete expansion can be used to obtain a reduction in turbine size when the turbine exhausts into a low-pressure condenser. And, by adding this turbine to single- and two-stage flashed-steam systems, the conversion efficiency of systems utilizing low- and high-energy wellhead sources, respectively can be improved. The Appendix outlines the analysis of the radial-outflow reaction turbine and leads to an expression for engine efficiency.