The effect of surfactant adsorption on surface tension, as well as associated thermodynamic concepts are introduced in a laboratory experiment designed for undergraduate students. Using a reliable and accessible method, students measure the surface tension of aqueous solutions at different concentrations of sodium dodecyl sulfate. Students collect data to estimate the critical micelle concentration and quantitatively determine the maximum surface excess using the Gibbs adsorption equation. Students subsequently determine the surface area per molecule of this surfactant at the liquid–air interface and learn how to generate adsorption isotherm curves.