[1] The Antrim is a brown to black, pyritic, highly laminated and organic-rich shale, from 60 to 220 feet thick.

It is overlain by the Bedford Shale, and underlain in some areas by the Jordan River Formation, and elsewhere by the Thunder Bay Limestone.

[2] Most natural gas production is in Antrim, Crawford, Montmorency, Oscoda and Otsego counties.

[3] Although the Antrim Shale has produced gas since the 1940s, the play was not active until the late 1980s.

Original gas content ranges from 40 to 100 standard cubic feet per ton.