Minimum values of 1/(Ka1[A]) that can be used in frontal analysis experiments to produce a given deviation from linearity in double-reciprocal plots for three-site systems at various combinations of affinities and various mole fractions of the highest affinity site (α1) when the mole fraction for the second highest affinity site (α2) is equal to 0.25. The mole fraction of the lowest affinity site (α3) was calculated by using α3 = 1 - α1 - α2; the x-axis extends in this case up to 0.75, which is the maximum allowed value for α1 if α2 is equal to 0.25. The affinities for the binding sites that were used in these calculations were (a) β1 = 1.00, β2 = 0.10, and β3 = 0.05; (b) β1 = 1.00, β2 = 0.25, and β3 = 0.125; and (c) β1 = 1.00, β2 = 0.50, and β3 = 0.25. These results were generated by using a modified form of eq. (10) that was based on eqs. (6)-(7) and developed for a three-site system.