HOUSTON — Oil companies, rig owners and refiners spread out across the Gulf Coast to look for damage from Hurricane Gustav on Tuesday, and some were already putting equipment and people back in place to resume operations.

Preliminary indications were that Gustav caused little damage to onshore and offshore facilities, though the full impact likely won't be known for a couple of days.

Still, the price of oil tumbled more than $8 a barrel in electronic trading on the New York Mercantile Exchange, suggesting traders were confident that the energy complex suffered only a glancing blow.

Many companies were flying over offshore sites in airplanes and helicopters Tuesday morning, checking for any obvious damage.

ConocoPhillips said remote monitoring of its Magnolia production platform about 165 miles off the Louisiana coast indicated it had not sustained significant damage.

"As weather conditions permit, we'll conduct a fly-over of the platform and south Louisiana assets to further assess their conditions," ConocoPhillips said in a statement.

The Houston-based oil giant also has two refineries in Louisiana — one near New Orleans, one near Lake Charles — and they both remained shut down.

Royal Dutch Shell said it would send a small number of staff Tuesday morning to installations in the Gulf that were out of the hurricane's path, though it noted it could take three to five days to resume full production in the Gulf.

In the days preceding Gustav, oil companies shut down virtually all oil and natural gas production in the Gulf, and the storm's threat halted about 15 percent of the nation's refining capacity based in the region.

The U.S. Gulf Coast is home to nearly half the nation's refining capacity, while offshore, the Gulf accounts for about 25 percent of domestic oil production and 15 percent of natural gas output.

Like ConocoPhillips, Anadarko Petroleum Corp., the largest independent deep-water producer in the Gulf of Mexico, said remote monitoring also indicated its offshore assets remained in placed as Gustav passed through the region Monday.

Valero Energy Corp. said late Monday that an initial assessment of its St. Charles, La., refinery, which turns 250,000 barrels a day of crude oil into gasoline and other fuels, found "no significant structural damage," although it was too soon to say when the plant's operations would restart.

Transocean Inc., the world's largest offshore drilling contractor, said Monday afternoon it appeared its three moored, semisubmersible rigs in the Gulf remained anchored in position during the storm.

Transocean said eight other rigs that used thrusters to move out of the storm's path also were safe and were moving back to their drilling locations Monday evening.