1. BP Statistical Review of World Energy, 68th edition. British Petroleum, London, England (2019).
http://www.bp.com/statisticalreview
2. Provisional Coal Statistics, Government of India, Ministry of Coal, Coal Controller’s Organisation, Kolkata.
http://www.coalcontroller.gov.in/pages/display/20-provisional-coal-statistics
3. Iyengar RK, Haque R (1991) Gasification of high-ash Indian coals for power generation. Fuel Process Technol 27(3):247–262.
https://doi.org/10.1016/0378-3820(91)90051-D
4. Grӓbner M (2015) Industrial coal gasification technologies covering baseline and high-ash coal. Wiley-VCH Verlag GmbH & Co., Germany
5. Roy RKD (1940) A critical study of some Indian coal ashes. Geol Survey of India 4(3):539–548