Equations for aerodynamic quantities of interest in equilibrium isentropic one-dimensional flows and for properties across plane showck waves in arbitrary of planetary gases are derived under the assumption that the gases obey the perfect gas law. This assumption restricts the range of applicability of the equations to conditions for which the onset of chemical dissociation or ionization has not been reached although no requirement for the gases to be calorically perfect is imposed. Analytic functions used to specify the variation of specific heats with temperature are consistent with the assumption that molecular vibrations behave like harmonic oscillators and are independent of rotational degrees of freedom. Simplified equations giving approximate results over more limited ranges of the variables are also presented. Sample comparisons of the aerodynamic behavior of a number of pure gases are made. It is shown that while some of the flow quantities characterizing aerodynamic flows are very sensitive to gas composition, the stagnation pressure coefficients for a number of gases differ by only a few percent from one gas to another.