A new surface equation of state with two thermodynamic parameters: the critical micellar concentration and the surface compressibility factor is presented, which comes from the experimental evidence and the equality of the Volmer's surface chemical potential and the bulk chemical potential at the diluted region under the symmetric activity coefficients convention. The new surface equation of state contains in its boundaries the exact relationship between the standard Gibbs energy of adsorption and the standard energy of micellization, and additionally allows the interpretation of the activity coefficient at infinite dilution in the light of the hydrophobic effect. (c) 2007 Elsevier B.V. All rights reserved.