Artificial reservoirs excavated from bedrock at depths of 200 to 500 feet offer the best prospects for underground storage of petroleum and its liquid products in Indiana. All the Paleozoic bedrock systems from Ordovician to Pennsylvanian contain potential reservoir sites in shale, siltstone, or limestone at places within the state. Suitable Ordovician rocks lie at proper depths beneath a greater area than the rocks of any other system. Competent beds for natural roof are more common in central and southern Indiana than in the northern part of the state. Thick glacial drift increases the difficulty of locating good storage sites in much of northern Indiana.