Twenty years ago geologists involved in the Appalachian Basin's oil and gas industry knew about the Devonian black shale called the Marcellus, its black color made it easy to identify. However, at the time, very few of these geologists were excited about the Marcellus Shale as a major source of natural gas. Wells drilled into the formation produced some gas but rarely in commercially viable volumes. Few if any in the natural gas industry suspected that the Marcellus would soon be a major contributor to the natural gas supply of the United States – large enough to be called a "super giant" gas field. (King, 2015).