Systematically characterizing the internal pore structure of coal has significance for producing coalbed methane efficiently. For this study, the pore structure of lignite, bituminous coal, and anthracite were investigated using low-temperature nitrogen adsorption (N(2)GA), high-pressure mercury intrusion (MIP), and low-field nuclear magnetic resonance (NMR). The N(2)GA method can accurately determine the distribution of adsorption pores and the specific surface area (SSA) of coal whereas the MIP method can accurately measure the size of seepage pores and pore volume. The pore size distribution curves generated by combining the N(2)GA and the MIP can portray the coal's micropore to macropore pore distribution more accurately than the distributions can be illustrated by either method alone. NMR is applicable for testing pores larger than 1 nm and can accurately measure porosity and pore volume but it cannot measure SSA. The N(2)GA method is more detailed and accurate than NMR for characterizing adsorption pores. (C) 2019 Published by Elsevier B.V.