US Gulf of Mexico oil and gas installations battened down Monday in advance of Tropical Storm Isaac as it headed toward the heart of the US refining and offshore energy industry.
About 78 percent of crude oil production and about 48 percent of natural gas production in the region had been shut in by 1900 GMT, the Department of Energy said.
Six of 12 refineries in the path of the storm had shut down or were shutting down, representing roughly 17 percent of total Gulf coast refining capacity, the department said.
Isaac, packing maximum sustained winds of 65 miles (100 kilometers) per hour, was less than 300 miles (480 kilometers) southeast of the mouth of the Mississippi River.
Expected to gain hurricane strength by Tuesday, it was headed northwest at 14 miles per hour toward Louisiana and neighboring states along the Gulf of Mexico, where 23 percent of the nation's crude and seven percent of its natural gas is produced.
The National Hurricane Center issued a hurricane warning for New Orleans and nearby areas, while states of emergency were declared in Alabama, Florida, Louisiana and Mississippi.
London-based BP shut down production at all of its oil and gas platforms in the Gulf, including its Thunder Horse platform, the world's largest offshore production and drilling facility, and evacuated staff.
US energy giant Chevron -- the second-largest oil producer in the Gulf behind BP -- moved staff on its offshore facilities out of Isaac's path.
ExxonMobil was evacuating offshore personnel and had shut down refining operations in Chalmette, Louisiana. Its Baton Rouge facilities in the state were operating at reduced rates.
Royal Dutch Shell reduced the operating rates at three refineries in Louisiana and one in Alabama.
Shell said the Capline pipeline, which transports crude oil to refineries in the Midwest, had been shut down late Sunday and will resume operations as weather conditions allow.
Refinery shut-ins, which reduced demand for crude coming to the market, weighed on oil prices.
The price of the New York WTI benchmark contract fell 0.7 percent to $95.47 a barrel, and London's Brent slumped 1.1 percent to $112.26.
Concerns over the storm were "fading," said John Kilduff, an analyst at Again Capital.
"It is not big enough to cause major damages to the energy infrastructures," Kilduff said.