The present paper deals with the competitive adsorption on activated carbon of three aqueous bi-solute systems (phenol/p-nitrophenol, phenol/p-chlorphenol, p-nitrophenol/p-chlorphenol) and of the tri-solute system phenol/p-nitrophenol/p-chlorphenol. In this context two experimental methods to evaluate the equilibrium characteristics for the adsorption of phenols on powdered activated carbon were used. The competitive adsorption data were statistically fitted on four models: the Langmuir competitive model, the Freundlich-Langmuir competitive model, and the Fritz-Schlunder model, the last one in two particular cases for the monosolute representation. The prediction for all models, excepting the Fritz-Schlunder model, were performed using only single-solute data, while the parameters for the Fritz-Schlunder model were obtained using both single and multi-solute data.