Potential natural gas resources in the New Albany Shale of the Illinois basin may be related to five key factors: relative organic content of the shale; relative thickness of the organically-rich shale; thermal maturity as related to depth of burial; presence of natural fractures; and type of organic matter. The shale that is organically richest is in southeastern Illinois and in most of the Indiana and Kentucky portions of the Illinois basin. The shales are thickest (about 400 feet) near the center of the basin in southeastern Illinois, southwestern Indiana, and adjacent parts of Kentucky. The area is deeply buried by younger rocks, and the organic matter has the highest thermal maturity. In addition, natural fault-induced fractures in the shale, which may aid in collecting gas from a larger volume of shale, may be present, since major faults along the Rough Creek Lineament and Wabash Valley Fault System cross the deeper part of the basin. Thus, this area near the basin center where the shale is thickest and rich organically and where fault-induced fractures may be present has the greatest potential for natural-gas resources. The eastern side of the basin, where the shale is organic-rich but thin, may have poor to moderate potential for additional discoveries of small gas fields similar to those found in the past. In western Illinois and the northern part of the basin, the potential is poor, because the organic content of the dominantly greenish-gray shale in this area is low. More exploration will be required to properly evaluate potential resources of natural gas that may exist in the New Albany Shale.