The Strategic Petroleum Reserve (SPR) is a supply of petroleum held by the United States Department of Energy (DOE) for emergency fuel. It is the largest emergency supply in the world, and its underground tanks in Louisiana and Texas have capacity for 797 million barrels.
The current inventory is displayed on the SPR's website. As of April 17, 2020, the inventory was 635.0 million barrels. This equates to about 34 days of oil at 2013 daily U.S. consumption levels of 18.49 million barrels per day or 64 days of oil at 2013 daily U.S. import levels of 9.859 million barrels per day.
However, the maximum total withdrawal capability from the SPR is only 4.4 million barrels per day, so it would take over 144 days (4.73 months) to use the entire inventory.