Coal was subjected to intensive grinding to produce submicrometer particles. This was done in two stages. Ultrafine coal produced by fluid energy mill grinding was further ground in a planetary ball mill or attritor mill. The grinding process was monitored by density gradient separation and surface area measurements. Conditions were established to produce coal in the 0.05-1 mum size range with 3 h of grinding. Several different slurry solvents were examined for grinding efficiency. Extensive accretion of coal particles to produce homogeneous particles was found to be a major problem. In several instances there appeared to be a low melting phase produced (approximately 65-degrees-C) which cemented the fine particles together during vacuum drying. The submicrometer coal also interacted with the surfactant used in density gradient analysis resulting in particle size dependent density distributions. Two cases were found that may have circumvented accretion problems : grinding in tetrabutylammonium hydroxide/pyridine/methanol and attritor milling in a methanol slurry at <-50-degrees-C.