b'PIPELINE EMERGENCY RESPONSE GUIDELINESSTORAGE RESERVOIRS The types of subsurface geologic formations or reservoirs commonly used for storing products under-ground include: depleted oil or gas fields, salt caverns and depleted aquifers.Depleted Fields Salt Formations Depleted Aquifers Depleted Oil or Natural Gas Fields Depleted oil and gas fields are commonly used to store natural gas. Of the approximately 400 active natural gas underground storage facilities in the U.S., about 80 percent are depleted natural gas or oil fields.Salt Caverns Salt caverns are commonly used to store crude oil and liquid petroleum gas (LPG). The U.S. Strategic Petroleum Res erve (approximately 700 million barrels of crude oil) is stored in 60 different caverns located in the Gulf Coast states of Texas and Louisiana.Depleted Aquifers Depleted aquifers are used to store approximately 10 percent of natural gas that is stored under-ground.They are found mostly in the Midwestern states. An aquifer is suitable for gas storage if the water-bearing sedimentary rock formation is overlaid with an impermeable cap rock.40 2023 by Pipeline Association for Public Awareness'