@misc{indiciae5ef1b5677c4b,
  title = {Coal exploratory drilling; a cost percentage comparison of three methods},
  author = {Robert G. Hobbs},
  year = {1979},
  doi = {10.3133/ofr791100},
  url = {https://pubs.usgs.gov/publication/ofr791100},
  note = {Source identifier: ofr791100}
}