BATON ROUGE, La. (AP) - Scientists with the University of South Florida say laboratory tests have confirmed that oil from a spewing Gulf of Mexico well has accumulated in at least two extensive plumes deep underwater.

The researchers said in Baton Rouge on Friday that tests confirmed their initial findings that were based on field instruments. BP PLC CEO Tony Hayward has said there was no evidence of large underwater plumes.

The researchers say the extensive layers of oil are sitting far beneath the surface miles from the site of the Deepwater Horizon explosion. The university is collecting data for the National Oceanic and Atmospheric Administration.

The lab tests are the most conclusive evidence yet in a vigorous scientific debate about where much of the oil is ending up.