SUBSCRIPTSA A , AB, BB d n C (0) W Y = system characteristic for in---.\ + CY (1x j terphase polycondensation, dimensionless. = terminal groups = continuous phase = dispersed phase = chain length = initial condition = molecular weight literature Cited A two-dimensional equation of state has been derived from the Hirschfelder-Eyring modification of the van der Waals equation and applied to the prediction of high pressure adsorption of pure and mixed hydrocarbons on charcoal. Equations are derived to express the thermodynamic equilibrium between a mixed adsorbate and gas, assuming the validity of the mobile fluid model for the surface phase. Solution of these equations permits the total adsorption and surface composition to be calculated for a mixed isotherm from pure component adsorption data. New experimental data are presented for high pressure adsorption of methane, propane, butane, and their mixtures on charcoal.