Deltaic and fluvial sedimentation processes have been recognized as primary dispersal mechanisms that operated to contribute sediments to the Chesteran depositional area in part of the Illinois basin of Illinois, Indiana, and Kentucky. As the fluvial cycle was initiated, erosion channels were incised into the underlying strata. Clastic sediments were delivered to the depositional area by the Michigan River system. The channel fill can be traced from its outcrop into the subsurface and across Kentucky for more than 100 mi (160 km). The fill can be projected with considerable success into areas where few tests have been drilled. Successful projections have been accomplished by making isopach maps of the channel fill. Once the distributary network is outlined, a direct relat on is apparent between the channel system and hydrocarbon accumulation within the Bethel Sandstone. The Midland, St. Charles, Barnsley, Luzerne, Sharon School, and Elk Creek fields occur within the distributary network.

All these fields are combination traps which are restricted to the channel fill and are localized by subsequent structural deformation. Of the several fields mentioned, Midland gas field is by far the largest. It was discovered in 1962 and, in 1968, had 59 gas wells producing from the Bethel Sandstone (early Chesteran). The gas reservoir is approximately 10.8 mi (17.4 km) long and 1.3 mi (2.1 km) wide and contains an estimated productive 542,257 acre-ft, which makes it the largest continuous natural reservoir in the Illinois basin. Estimated original reserves are placed at 163 billion cu ft of gas; approximately 51 billion cu ft had been produced through 1967. Maximum productive sandstone exceeds 180 ft (55 m) in thickness.