A multicomponent adsorption equation is developed from a modified Dubinin isotherm for the pure components. This isotherm equation satisfies thermodynamic consistency requirements while being easy to use and predicts binary and ternary mixture data from pure component parameters. A description of the effect of coadsorption of bulk gas on a trace adsorbate is also possible. Further, successful mixture predictions from the isotherm show that it significantly reduces hitherto reported large, apparent nonidealities which are believed to be associated with energetic heterogeneity in adsorption.