Because most commercially available surfactants consist of mixtures of surfactant components, an understanding of mixed surfactant sorption behavior in the presence of natural materials may be essential for optimal design of surfactant-based industrial processes or environmental remediation applications. This paper presents a new predictive numerical model of surfactant sorption which can be used to assess the sorption behavior of nonionic surfactant mixtures based on a minimal set of physically intuitive, measurable parameters. The model is based on a chemical equilibrium formulation and can predict the sorption behavior of very broadly distributed mixtures containing 40 components or more. Formulation of the model is presented, and solution methods are discussed. The influence of model parameters on isotherm shape is examined, and application of the model to prediction of mixed sorption of a binary surfactant mixture is presented, An extension of the model which includes multiple surface site types is discussed.