The Brunauer-Emmitt-Teller (BET) equation for multicomponent adsorption was derived using assumptions similar to those used in the derivation of the original BET equation. In addition to the assumptions used in the derivation of the original BET equation, the BET equation for mixture adsorption was obtained by assuming that multilayer adsorption in a given layer is independent of the identity of the molecule adsorbed beneath it in the previous layer. The adsorption and desorption processes were considered to be reactions and the expression for the equilibrium concentration on surface was obtained using the equilibrium constants of the reactions. The performance of the BET equation derived for mixtures was compared with that of the widely used extended Langmuir equation using some selected binary adsorption isotherm data shown in the literature. The performance of the BET equation derived in this work was better than that of the extended Langmuir equation in the prediction of adsorbed phase concentrations and adsorbed amounts for the binary systems considered in this work.