"HyperCoal" (HPC) is the ashless coal produced by thermal solvent extraction; the extraction yield is a key factor in HPC production. The extraction yield varies depending upon the properties of the coals and the solvent used. For a wide range of coals, the extraction yields at 360 degrees C have been successfully estimated by a multiple regression analysis, using the values of ultimate and proximate analyses. The equation consists of volatile matter/O% (or O%), C/H, and a function of S%; a correlation coefficient of r = 0.790 was obtained for the extraction yield with 1-methyl-naphthalene (1-MN) for 76 coals. When the polarity of the extraction solvent was increased, the effects of O% decreased, while that of C/H did not change. With regard to coals with an O% less than 8.2, the extraction yield of 1-MN correlated only with the C/H value. These results suggest that the C/H value is the main factor for a high extraction yield.