Preliminary lab results show two oil samples taken on the Louisiana coast are from BP's 2010 Gulf spill, state officials said.
The oil was discovered on Elmer's Island, said spokeswoman Olivia Watkins of the state Coastal Protection and Restoration Authority.
"There are additional samples in the testing pipeline. However, the proximity of these other oil mats is very close to those that tested positive for BP oil," she told CNN in an e-mail.
Samples also are being taken at other locations on the coast, according to Watkins.
In the wake of Hurricane Isaac, state officials reported tar balls and a large oil mat along the Gulf shore south of New Orleans. It's not clear whether the hurricane swept tar balls ashore or exposed them under the sand, U.S. Coast Guard Petty Officer Bill Colclough said. The U.S. Coast Guard reported finding three oiled birds in the area on Monday.
BP said Wednesday it was heading to the coast to test whether tar balls and oil are from the 2010 spill.
BP spokesman Ray Melick said the area is one where BP teams were already helping with cleanup from the 2010 spill before Isaac arrived.
"There's a lot of oil out there that may not be ours," Melick said.
The coastal protection authority is coordinating with other state agencies to test the contents.
The area is near Fourchon Beach and Grand Isle.
The same area was heavily affected by the spill, which happened in April 2010 after an explosion aboard the Transocean Deepwater Horizon oil rig in the Gulf of Mexico. BP had contracted the rig, which had 126 workers on it, 11 of whom are presumed dead.
Colclough said pollution after a hurricane is expected because the force of the storms can bring oil and other debris to the surface.