The theory for the compression of an adsorbed soluble monolayer was extended to systems containing two surfactants. This theory was confirmed experimentally for decanoic and dodecanoic acid mixtures, The parameters needed to describe the compression curves were estimated from the behavior of the pure systems, For doing this, solutions of decanoic and dodecanoic acid were prepared in such a way that the equilibrium adsorptions were nearly the same. Also, in the mixed systems, the sum of the adsorption of both components were equal, allowing reasonable prediction of the parameters needed to describe the experimental results, The agreement between theory and the experiments is good, From these experiments, we can obtain the surface elasticity for mixed monolayers as a function of the effective time.