He said the release represented less than 5 percent of the nation’s strategic oil reserve.

The action is also a response to market uncertainties after the June 8 meeting of the Organization of the Petroleum Exporting Countries, which failed to reach an agreement on increasing production quotas. After the meeting, Saudi Arabia and the Persian Gulf states agreed to pump as many as 1.5 million more barrels of crude per day, but those countries cannot produce sufficient supplies of the high-quality crude that Libya normally exports.

News of the release sent oil prices sharply down. West Texas Intermediate, the United States benchmark crude, fell $4.39 a barrel to $91.02. The European benchmark, Brent crude, fell even more.

Even before Thursday’s announcement, the average price of a gallon of regular gasoline had fallen to $3.61, from $3.83 a month ago, according to the AAA Daily Fuel Gauge Report. A year ago, the price was $2.74 a gallon.

Some in the oil industry said the move was unnecessary.

“Releasing oil from the Strategic Petroleum Reserve today, when gasoline prices are falling and there is no supply shortage, makes no sense and weakens our economic and national security,” said Charles T. Drevna, president of the National Petrochemical and Refiners Association.

The 727-million-barrel Strategic Petroleum Reserve was established by the United States after the 1973-74 Arab oil embargo to provide presidents with an emergency response to similar disruptions in commercial supplies that threaten the economy and national security.

In addition to the 1991 release, in September 2005 President George W. Bush ordered a drawdown after Hurricane Katrina disrupted oil supplies from the Gulf Coast region. The 1991 release was about 17 million barrels; the 2005 hurricane release was 21 million barrels.

The coordinated move came after more than two months of quiet diplomacy involving major industrialized countries, Saudi Arabia, Kuwait and the United Arab Emirates. American officials visited Saudi Arabia in May to consult about the anticipated action and to seek assurances that the Saudis would also increase production to help fill the gap left by the Libyan disruption. The White House said that President Obama spoke with King Abdullah of Saudi Arabia at least twice about the issue since the end of April.