A set of 466 individual full channel samples (coals, coaly shales and partings) of thirteen Bulgarian coal deposits, as well as vitrain lenses, gagatite and coalified woods embedded in sedimentary rocks have been analyzed by atomic emission spectroscopy. The deposits consist of lignites, subbituminous and bituminous coals. The average boron content ranges from 15 to 164 ppm in the coals. The boron content of the individual coal samples ranges from 2 to 164 ppm. About 86% of the samples have a B content from 2 to 110 ppm, which corresponds to the most probable interval of concentration for coals worldwide. The boron content is not related to rank. The lignites have the lowest boron content. Some of the vitrain and xylain samples studied are enriched in boron in comparison with the whole-coal samples. Boron occurs in both organic (B(org)) and inorganic (B(inorg)) forms. Excluding one deposit, the boron content in the ash correlates negatively with the ash content, whereas in coals it usually slightly increases with increasing ash content. Organically associated B dominates in the low-ash coals and in the deposits enriched in boron. The coals of the Burps deposit have the highest B content, which is in agreement with the geological evidence for marine influence during the early stages of coalification. The distribution of B is also independent of other geological factors.