Lawrence O. Anna Steven M. Condon Neil S. Fishman Timothy C. Hester Paul G. Lillis Elisabeth L. Rowan Ronald Charpentier Troy A. Cook Robert A. Crovelli Timothy R. Klett Christopher J. Schenk Jennie L. Ridgley 2008 Application of a geology-based assessment methodology by the U.S. Geological Survey resulted in an estimated mean of 6,192 billion cubic feet of shallow biogenic (continuous) undiscovered gas in the North-Central Montana Province. Oil, gas, and natural gas liquids in conventional accumulations were not assessed. application/pdf 10.3133/fs20083036 en U.S. Geological Survey Assessment of undiscovered biogenic gas resources, North-central Montana Province reports