Analytical expressions for optimum power extracted in a MHD generator with constant channel width and constant electrical conductivity proposed by Neuringer was investigated for a range of subsonic and supersonic inlet Mach numbers. Characteristics of fluid-dynamical variables, optimum power extracted and the voltage drop in the external load were studied for a range of Mach numbers and interaction parameters. It was observed that the characteristics of voltage drop across the load with the interaction parameter differed significantly for subsonic and supersonic inlet Mach numbers. For each subsonic inlet Mach number, there exists a critical value of interaction parameter beyond which there is an abrupt change in terminal voltage, and fluid-dynamic variables. Also beyond this critical interaction parameter, the flow at the exit plane is choked. Supersonic inlets do not display the presence of such a critical interaction parameter or choking at the exit plane. (C) 2008 Elsevier Ltd. All rights reserved.