Energy companies began assessing their oil rigs, refineries, and pipelines for damage on Tuesday, a day after Hurricane Gustav hit the U.S. Gulf coast in the first big threat to U.S. fuel supplies since 2005. Some companies already were putting equipment and personnel back in place to resume operations, and early indications were that the storm caused little damage to onshore and offshore facilities, though the full impact likely will not be known for a few days. Most energy production in the Gulf of Mexico—which accounts for one-quarter of U.S. oil output—remained shut down Tuesday after the storm. On shore, about one-third of the country's refining capacity was either shut of slowed by Gustav. “Preliminarily, we don't know of any major damages at this time,” John Rodi, deputy regional director of the U.S. Minerals Management Service, said Tuesday. Many companies were flying over offshore sites in airplanes Tuesday morning, checking for obvious damage. One of the next steps will be getting people aboard the offshore facilities for more detailed inspections, including checks of underwater equipment. “We are beginning the process of getting our people and resources into place to check these facilities and will be doing aerial surveys, but it takes time to do this,” said Chevron Corporation spokesman Mickey Driver. The approach of Gustav had helped support oil prices, which plunged Tuesday by more than $7 to below $108 a barrel on the New York Mercantile Exchange—a drop of 26 percent from record highs above $147 in July. Prices fell as traders bet that the storm spared the energy industry the lasting damage inflicted by Hurricanes Katrina and Rita in 2005.