Upper Devonian black shales of the eastern United States have long been known as major gas producing shales. Our solid state C-14 NMR studies of the kerogen in shales of the Lower Huron Member of the Ohio Shale have demonstrated a regional gradient in carbon aromaticity that parallels both the known metamorphic gradient and trends normal to inferred paleoshorelines. The kerogen is essentially coal-like throughout most of the basin with aromaticities of 0.5C or greater. Large changes in carbon aromaticities are observed along an east-west line in our study area, the western half of the basin where maturation levels are low. We believe that the eastward increase in aromaticity is related to increased contributions of vascular plant remains as one approaches paleoshorelines. It is likely that a large proportion of the natural gas in these shales evolves fro low-rank maturation of the coaly kerogen.