The National Hurricane Center in Miami downgraded Isaac to a tropical storm as it moved inland. It struck the southern Louisiana coast as a Category 1 hurricane.
U.S. Geological Survey instruments in Louisiana indicated the Mississippi River flowed backward for about 24 hours as Hurricane Isaac made landfall.
USGS Director Marcia McNutt said such events are brief but served as another indicator of the importance of early warning systems.
International energy companies with installations along the southern U.S. coast evacuated personnel and shut operations ahead of the storm. Global analytical company IHS said about 85 percent of the production platforms in the Gulf of Mexico were closed because of Isaac.
The Houston Chronicle reports that energy companies working in the gulf were struggling to cope with the storm because of heavy rains and power outages. About 1 million consumers were without power in Louisiana, Mississippi, Alabama, Arkansas and Texas.
Crude oil prices fell Wednesday though gasoline prices were high despite adequate stockpiles. Ben Brockwell, director of the Oil Price Information Services, said gasoline purchases by retailers just ahead of the storm may be a factor when examining retail prices, the Chronicle adds.