Development and validation of a three-dimensional, two-phase, dual porosity, fully implicit, compositional coalbed simulator are presented. Multicomponent sorption equilibria using a thermodynamically consistent ideal adsorbed solution (IAS) theory is implemented to the simulator using a non-equilibrium sorption formulation. The sorption model accounts for the non-ideality of the free gas phase, as partial fugacity of the gas component is calculated using the Peng-Robinson equation of state. Model predictions of multicomponent sorption of methane, nitrogen and carbon dioxide mixtures on the coal are found to be in good agreement with experimental measurements. The transport component of the compositional coalbed simulator is verified using an existing two-phase coalbed simulator.