Coal samples in the form of randomly oriented aggregates were obtained from the Pennsylvania State University Coal Bank for the purpose of thermal conductivity measurements. Samples represented 55 locations from throughout the United States and included 6 lignites, 10 subbituminous coals, 36 bituminous coals, and 3 anthracite samples. Matrix thermal conductivities measured at 22 ¿C in the laboratory ranged from 0.22 to 0.55 W/m ¿K, with an arithmetic mean of 0.33 W/m ¿K and a standard deviation of 0.07 W/m ¿K. The thermal conductivity of lignites, subbituminous, and bituminous coals is controlled by composition and can be predicted by a three-component (moisture, ash, and carbon+volatiles) geometric mean model with a rms residual of 6.1%. The thermal conductivity of bituminous and anthracite samples was found to be positively correlated with matrix density. With the exception of three anthracite samples, rank was not correlated with thermal conductivity nor was the ratio of carbon to volatiles. The relatively high thermal conductivity of three anthracite samples (mean of 0.49 W/m ¿K) may have been related to graphitization. ¿ American Geophysical Union 1996