Campbell, G.G.; Brandenburg, C.F. & Boyd, R.M. Preliminary evaluation of underground coal gasification at Hanna, Wyo. [Investigation of feasibility of gasifying subbituminous coal underground; H/sub 2/-rich gas having heating value of 100-150 Btu/sel produced], report, October 1, 1974; (https://digital.library.unt.edu/ark:/67531/metadc1052373/m1/1/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .