Baton Rouge, Louisiana - 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."

Definition: In hydrodynamics, a plume is a column of one fluid moving through another. Several effects control the motion of the fluid, including momentum, diffusion, and buoyancy (for density-driven flows). When momentum effects are more important than density differences and buoyancy effects, the plume is usually described as a jet.Usually, as a plume moves away from its source, it widens because of entrainment of the surrounding fluid at its edges. Plume shapes can be influenced by flow in the ambient fluid (for example, if local wind blowing in the same direction as the plume results in a co-flowing jet). This usually causes a plume which has initially been 'buoyancy-dominated' to become 'momentum-dominated' (this transition is usually predicted by a dimensionless number called the Richardson number).