All oil pools extending from El Dorado, Kansas, to Oklahoma City along the Nemaha granite ridge and the southern extension of that line of folding have important oil accumulations at an unconformity beneath the Pennsylvanian shales. This relation, together with evidence from later folds in the region, furnishes data from which the approximate date of oil migration and accumulation can be determined. Consideration of various possible sources for this oil indicate that it was not generated until long after the sediments were deposited, and that its source can not logically and consistently be sought in the rocks in the immediate vicinity of the pools. Generation of the oil by metamorphic agencies during the Appalachian revolution and its migration, in some regions through l ng distances, to its present reservoirs through porous carrier beds is a suggested hypothesis which seems to accord better with the data from the fields than do any of the hypotheses of local origin of the oil.