The flow fields of supersonic, nonequilibrium corner expansion flows of ionized gases have been solved numerically, for three different gases, using the method of characteristics. Special attention has been given to the effect that the gas mass and its ionization potential have upon the solution obtained. It was found that the ratio between the atomic mass of the element considered and its ionization potentialma/&Vthgr;I, plays an important role in establishing thermal equilibrium. Gases having a small value ofma/&Vthgr;Iwill approach thermal equilibrium at a faster rate than those having a larger value ofma/&Vthgr;I. On the other hand, the approach to chemical equilibrium is controlled by the recombination rate which is strongly temperature dependent. Therefore, fast reduction in temperature, in the expansion field, promotes a rapid approach to chemical equilibrium. The effect of the electron‐atom collision cross section &sgr;ea, on the numerical results obtained, is also studied. It is shown that accurate knowledge of &sgr;eais required to evaluate the plasma electronic properties (Teand &agr;), but even a rough estimate of &sgr;eais sufficient for the evaluation of the gross properties of the plasma (p, &rgr;, andT).