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While certain rheological-structural properties of some coals have been determined at elevated temperatures, Insufficient data exists to realistically characterize the structural behavior of coal under in situ gasification conditions. Much of the data available is for crushed, crushed and compressed, or otherwise modified conditions of coal from its natural state. The stresses and displacements due to the in situ gasification process and its gradients in the tectonic stress field vary over a wide range of values, thus necessitating the determination of the thermoviscoelastic properties of the Pittsburgh coal. The objectives of this research are: — Determine the mechanical properties (E, G) of Pittsburgh coal at elevated temperatures into the softening and coalescent stage. — Develop viscoelastic models of the Pittsburgh coal throughout the temperature range into the softening and coalescent stage by components of Kelvin and Maxwell elements.