Contents, modes of occurrence and origin of Cl and Br in individual coal samples from 34 deposits worldwide (Bulgaria, Australia, the United States, Japan, Canada, South Africa, China, and Ukraine) were studied. Some relationships of Cl and Br contents with chemical and mineral composition, rank, age, ash yield and geographic location of coals are described. Despite of similar chemical and geochemical properties of Cl and Br some distinct differences in the association, behaviour and occurrence of both elements in coal were found and discussed. Chlorine and Br in coal may occur, in decreasing order of significance, as organic compounds, as impurity components in the crystalline and amorphous inorganic constituents, in the fluid constituents and as discrete minerals. Both elements could have an organic occurrence and association with water-soluble (mainly ionic) and water-insoluble (ionic and covalent) organic combinations. Chlorine was identified as an impurity in minerals and inorganic phases such as clay minerals, mica, feldspars, polyhalite, gypsum, siderite, volcanic glass, phosphates and other carbonates and sulphates. A characteristic Br association with illite and to a lesser extent with mica, kaolinite and Fe bearing minerals was also found. Water molecules, hydroxyl groups and exchangeable cations in various minerals play a leading role for the inorganic occurrence and distribution of both elements. Discrete Cl minerals such as sylvite, halite, chlorapatite and probably carnallite were also identified. Significant amounts of Cl ions may associate with solutions in the inherent moisture of the coal mesoporosity. Limited proportions of both elements may also occur in gas-liquid inclusions of different solid phases. The favourable conditions for Cl and Br enrichments in coal are also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.