HyperCoal is an ash- free coal produced by extraction with an industrial solvent at temperatures around 360 C, which can be fed directly to gas turbines. We searched for more powerful solvents to extract low- rank coals, such as sub- bituminous coal. Polar materials were successfully concentrated from a polar industrial solvent, crude methylnaphthalene oil ( CMNO), by extraction with a mixture of methanol and water or aqueous HCl. The soluble fraction obtained using the former ( MW- S) extracted 73 wt % ( daf) of Wyodak Anderson sub-bituminous coal at 360 C, while that obtained using the latter ( AC- S) extracted 63 wt %. These extraction yields were much higher than those with CMNO ( 43 wt %), indicating that fractionation concentrated the materials that dissolve the constituents of coal. MW- S contained more indole than AC- S. The results of addition tests suggested that indole had a greater ability to extract coal constituents than quinoline. In addition, the addition of 5 wt % methanol to a mixture of 1-methylnaphthalene, indole, and quinoline ( 30/ 20/ 50 wt %) increased the extraction yield from 58 to 69%, which was close to the yield of MW- S ( 73%). Therefore, the high extraction yield of MW- S can be explained by not only the composition of the nitrogen- containing polar materials in MW- S but also the presence of methanol.