TOUGH2 code; equation of state (EOS) module for TOUGH2 is developed; the simulator (called here COALTOUGH); governing equations: TOUGH2 formulation; integrated finite difference method (IFDM) or finite volume method; differential form of the mathematical model; reaction models; approximate densities for the main components of coal; properties of gases and coal; experimental data for New Zealand and Australian coal samples; model parameters; New Zealand; Australia