Competitive adsorption of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (TMDD) with octanesulfonic acid Na+ salt, decanesulfonic acid Na+ salt, dodecanesulfonic acid Na+ salt, and protonated and deprotonated octanoic acid was observed using sum frequency generation (SFG) spectroscopy. SFG spectroscopy allows the direct observation of the relative surface density of TMDD. Various models of competitive adsorption for mixed surfactant systems were compared. Models taking into account kinetic, steric, and electrostatic factors were compared to the experimental data. For systems not undergoing a two-dimensional phase transition, a model incorporating steric and kinetic factors provided the best agreement with experimental observations.