The Merchant Marine Act of 1920 (popularly known as the Jones Act) "requires that all goods transported by water between U.S. ports be carried in U.S.-flag ships, constructed in the United States, owned by U.S. citizens, and crewed by U.S. citizens and U.S. permanent residents." (Wikipedia)
The Jones Act could adversely affect that handling of the oil spill at BP's Deepwater Horizon if it prevented foreign flagged vessels from participating in the cleanup efforts. Reportedly, this has not yet been a problem:
No Jones Act waivers have been required for the 15 foreign-flagged vessels currently in operation in the Gulf of Mexico. A foreign flag vessel can conduct certain operations as part of the flotilla if it is an oil spill response vessel and meets the requirements of 46 USC § 55113.
Even so, Ted Frank is critical--I think correctly--of the Obama administration for not moving sooner on the issue:
For the record: in Hurricane Katrina, the Bush administration was able to get Jones Act restrictions that interfered with help from international ships waived on Day 3; for Deepwater Horizon, where international help is much more critical due to shortages of domestic shipping able to engage in oil-skimming, it's 60 days in, and the Obama administration still hasn't waived the Jones Act. Keith Hennessey, who was involved in the Bush White House process, explains; see also WSJ, Olson, Bader.
Given that the only purpose of the Jones Act is 1920-era protectionism of special interests against foreign competition at the expense of the American consumer, and given that this could be done with the stroke of a pen, this should be a much bigger scandal. But it appears that the Obama administration is stonewalling on the issue by falsely claiming that a Jones Act waiver would not make any difference; after all, if they do waive the Jones Act, and the public sees how much additional help European allies could have been providing all along, the comparison with the Bush administration will become even more unfavorable.
