1. The underground gasification of coal;Elder,1963
2. A current appraisal of underground coal gasification;A.D. Little, Inc.;NTIS, PB-209 274,1972
3. A field test of underground combustion of coal;Raimondi;J. Petrol. Technol.,1975
4. Comparison of results from underground coal gasification and from a stirred-bed producer;Fischer,1975