A detailed study of the Venango district conducted during the past 5 years by the Pennsylvania Topographic and Geologic Survey has shown that all the oil-producing areas of that district are primarily stratigraphic. They may be classified, on the basis of shape and trend, into three types, each of which is confined to the upper, middle, or lower sandy formation of the Venango group. The first type is characterized by small irregular pools tending to be aligned approximately perpendicular to the ancient shore line. The second type is characterized by more uniform, sheet-like sands which pinch out abruptly along a smooth and fairly straight edge parallel with the ancient shore line. The third type is characterized by long, narrow, and in many places very pebbly bars which a e either single or multiple and approximately parallel with the ancient shore line. Pools typical of each of these types are described.