The approach to the derivation of the equation of state of a surface monolayer developed earlier and based on the excluded area concept was extended to multicomponent systems. A universal differential equation of state was derived. Its particular solutions in the zeroth and first approximations were the generalized van Laar, Frumkin, and van der Waals equations. The second approximation gave a new, more accurate equation of state applicable to a wider range of states. A procedure for calculating state parameters via the second and third virial coefficients was developed.