The relationships between the inverse of the characteristic residence time a(q) which is a measure of the strain rate at extinction, the ＇＇scalar dissipation rate＇＇ at extinction chi(q), the adiabatic dame temperature T-st, and the stoichiometric mixture fraction Z(st) in diffusion flames are examined. Numerical calculations are performed to determine the structure and critical conditions of extinction of diffusion dames stabilized between counterflowing streams, one containing methene and the other containing oxygen. These reactant streams are diluted with nitrogen or with nitrogen and argon. In the flame the value of the scalar dissipation rate is found to vary over a wide range and its value evaluated at Z(st) is used to characterize the system. At constant values of T-st the values of a(q) and chi(q) are found to decrease with decreasing values of Z(st). The value of chi(q) decreases at a faster rate than that of a(st). At constant Values of Z(st) the values of a(q) and chi(q) are found to decrease at the same rate with decreasing values of T-st. At constant values of both T-st and Z(st) the values of a(q) and chi(q) are found to be constant for various concentrations of reactants and inert species in the counterflowing streams.