Previous investigations have demonstrated that a compressible reacting mixing layer can develop two instability modes in addition to the more common central mode that exists unaccompanied in incompressible nonreacting flows. These two additional modes are termed “outer” because of their association with the fast and slow free streams. Numerical simulations have shown that mixing layers dominated by outer modes have a lower global reaction rate in comparison to a flow structure governed by the central mode. Therefore, the presence of these modes has important consequences for applications in supersonic combustion. Results are presented from a parametric study of the compressible reacting mixing layer’s regime space using linear stability analysis. The focus of our work is to develop a better understanding for the combined effects of compressibility, heat release and the ratios of density, equivalence, and velocity on the instability characteristics of each mode and on the structure predicted to result in a turbulent reacting mixing layer. ©1998 American Institute of Physics.