A theoretical model has been developed to explain the unexpectedly long communication ranges of over 300 m obtained, and the marked polarization effects observed, during recent radio transmission measurements in a conductor-free area in a coal mine at frequencies in the range of 57.5 to 920 kHz. The model is based on a dipolar cylindrical TEM mode of propagation, with E vertical and H horizontal, in a low-conductivity horizontal coal seam bounded by high-conductivity rock. The best overall fit to the experimental data over the frequency range 57.5 to 920 kHz is found for coal and rock conductivities of 1.4 × 10−4 mho/m and 1.0 mho/m, respectively, for an assumed coal dielectric constant of 7. A better fit to the data at 57.5 kHz can be obtained if, in the model, the conductivity of the surrounding rock is allowed to be high for only a short distance above and below the coal seam and of a substantially lower value elsewhere. If the coal conductivity is changed from 1.4 × 10−4 mho/m, which is near the lower end of the range of expected values for bituminous coals, to 1.0 × 10−2 mho/m, which is near the upper bound of values for such coals, the attenuation is markedly increased with corresponding reductions in communication range.