The East Bokaro CBM block is one of the most promising area for bituminous rank coal bed methane production in India. This work investigates the coal seams of Barakar and Karharbari Formations for measuring their in-situ gas content, maceral composition, thermal maturity (Ro%), gas composition and its controlling parameters. The depth of coal core samples laterally varies from 394.0 to 1091.05m and thickness of coal seams varies from 0.45 to 20.9m. The coal samples are vitrinite rich, thermally matured and potential source rock of methane gas. Large amount of desorbed gas (1.57 to 10.50cc/g) contributing to in-situ gas content (2.2 to 11.8cc/g), signify control of overburden pressure to retain gas in coal seams. The desorbed gas was analysed for molecular as well as isotopic composition and correlated with the petrographic constituents and vitrinite reflectance of the coal beds. The large quantity of methane concentration compared to C2 and C3 and ratio of C1/(C2+C3), indicates thermogenic origin of coal seam gas during bituminisation and de-bituminisation stages. The increase in percentage of C1 with Ro% implies that methane concentration increases proportionately with coal rank. Enriched ä13C1isotopic values and presence of C2 and higher hydrocarbons indicates the possibility of mixing of methane, generated at high temperatures, with C2+ hydrocarbons during transport and storage. The paper presents various relations suggesting in-situ gas content and its composition controlled by thermal maturity and maceral group of coa
