The complex equilibria in three-component additive systems composed of A, B and C components have been investigated. In these systems the pair-pair interactions take place through formation of chemical species with an arbitrary composition, following the scheme of reactions: (1) By changing the total concentration of one of the components and keeping constant the concentrations of others, in terms of reactions (1) between all the components, their equilibrium concentrations a, b and c are mutually correlated. As a characteristic of the variation of equilibrium parameter (concentration) of one component, let admit A, at infinitesimal small perturbations, for example at the total concentration variation of the same component A under the invariability of other total concentrations B and C, the following derivative has been used: (2) The derivatives of type (2) are entitled in this paper as the stability coefficients, being symbolized by the letter S. In the brackets, the function A is differentiated in respect to lna, under the constancy B and C, noted in the equation (2) by subscript symbols. The higher is the stability coefficient S, the more strongly the system opposes to changeability of the equilibrium parameter (concentration) of one of the components to specified small perturbations. Therefore, the stability coefficients S characterize also the buffering properties of the system. According to the definition, the derivative of (2), when the function and the variable in respect to which is differentiated refer to the same component, is analogical with the “classical” buffering capacity. In this paper, the analytical expressions of the stability coefficients for three-component additive systems, in which the pairs-pairs chemical interactions take place, have been deduced. The complete set of stability coefficients for the system (1) can be presented in the form of the matrix : (3) The stability coefficients as the elements of matrix are valid in terms of constancy of the total concentrations of all components, except the examined one. Thus, the stability coefficients (2) characterize the stability (insensibility, inertia) of the equilibrium parameter, for example lna in respect to variation of A (B or C) under the condition that the lnb and lnc may vary. The practical applicability of the derived relations for the control and regulation of the chemical composition of multicomponent systems has been investigated.