In an electrogasdynamic generator a portion of the enthalpy of a high velocity gas flow is converted directly into electrical energy through forcing unipolar charge carriers against an electric field. In a first attempt we try to describe this process by use of a one-dimensional mathematical model with an adiabatic flow. An exact analytic equation is derived for this case. Assuming the interaction between the charge carriers and the gas to be a perturbation of the first order this equation can be solved analytically. The zero order perturbation, i. e. constant thermodynamic state of the flow, agrees with previous analyses. It is found that this is an adequate approximation for the linear model. A complete analysis of a cylindrical EGD generator must however take into account the radial electric field due to the space charge and the losses due to radial diffusion and mobility. A tentative investigation of a three dimensional axially symmetric model has therefore been made, including a survey and criticism of some earlier analyses.