The U.S. plans to release 172 million barrels of oil from its Strategic Petroleum Reserve, more than 40% of a wider release coordinated with allies, to help dampen prices spiked by supply disruptions from the U.S.-Israeli war on Iran.

The U.S. sale, announced late on Wednesday, is part of a 400-million-barrel release by members of the International Energy Agency. The U.S. Department of Energy said the U.S. drawdown would begin next week and take about four months.

The SPR currently holds about 415 million barrels, most of which is high sulfur, or sour crude, that U.S. refineries are geared to process. The crude is held underground in hollowed-out salt caverns on the coasts of Texas and Louisiana that can store 714 million barrels.

Here is how U.S. presidents have tapped the SPR in times of war:

RUSSIA INVADES UKRAINE

In March 2022, the month after Russia invaded Ukraine, former President Joe Biden ordered the release of 180 million barrels over six months - the largest sale ever from the emergency stash. Biden, and later President Donald Trump, slowly bought some oil to replenish the reserves, but little has been added back as Congress needs to provide more money to do so.

ATTACK ON SAUDI ARABIA

Yemen's Iran-aligned Houthis attacked Saudi Arabia in 2019, prompting the shutdown of more than half the crude output in the world's largest exporter. Trump, then in his first term as president, said his administration stood ready to tap the SPR if needed. Ultimately that did not happen, as oil output recovered quickly from Saudi Arabia's Abqaiq plant and Khurais field.

LIBYA CIVIL WAR

In June 2011, former President Barack Obama ordered the release of 30 million barrels of oil from the reserve to offset disruptions to global markets from civil war in oil producer Libya. That sale was coordinated with the Paris-based IEA, resulting in an additional 30-million-barrel release from other member countries.

OPERATION DESERT STORM

In 1990-1991, after the Iraqi invasion of Kuwait, former President George H. W. Bush sold about 21 million barrels in two phases. In October 1990, the U.S. ordered a 3.9-million-barrel test sale. In January 1991, after U.S. and allied warplanes began attacks against Baghdad and other military targets in OPEC-member Iraq as part of Operation Desert Storm, Bush ordered the sale of 34 million barrels, of which half was sold.