"Contrary to conventional wisdom, such early researchers as Ashley and Reeves in their studies of eastern oil shales noted that weathered oil shales gave higher oil yields than did fresh shales. Preliminary work in Indiana partly supports that observation. Oil yields from 20 weathered oil-shale samples were comparable to yields from fresh samples. Samples of weathered shale from four locations of exposed shale overlying the Springfield Coal Member of the Petersburg Formation (Pennsylvanian) gave an average of 11.8 gallons/ton (9/t), and the average oil yield for 70 fresh samples of the same unit was 11.4 g/t. Oil shales above the Houchin Creek Coal Member of the Petersburg Formation gave an average of 10.9 g/t for 10 weathered samples compared with 7.2 g f t l or 22 fresh samples. According to limited data, weathered oil shales above the Colchester Coal Member of the Linton Formation (Pennsylvanian) gave an average of 10.3 g/t for three samples compared with 2.2 gft for six fresh samples. Although slight weathering increased yields, extreme weathering led to reduced oil yields. Weathering tends to increase water yields dramatically; it decreases sulfur contents and brings about other chemical changes. Weathered samples of the New Albany Shale (Devonian and Mississippian) were less consistent. Moderately weathered shales of the Henryville Bed of the Clegg Creek Member showed slight decreases in oil yields, and severely weathered samples of the Henryville and other beds of the Clegg Creek Member showed marked decreases (greater than 50 percent). Early stages of weathering seem to make kerogen more amenable to oil production in Pennsylvanian shales than in New Albany shales. This difference may result from differences in type of organic materials and depositional environments; the New Albany Shale is mainly euxinic marine, and the Pennsylvanian shales are from varied environments dominated by terrestrial organics"